Speaker Mike Johnson’s decision to publicly release thousands of hours of Capitol security footage from Jan. 6, 2021, has fueled a renewed effort by Republican lawmakers and far-right activists to rewrite the history of the attack that day and exonerate the pro-Trump rioters who took part.

Mr. Johnson’s move last week to make the footage available — something the far right has long demanded — came as he tried to allay the anger of hard-line Republican lawmakers for working with Democrats to keep the government funded. Now, some of the same people who were irate about that decision are using the Jan. 6 video to circulate an array of false claims and conspiracy theories about the largest attack on the Capitol in centuries.

Representative Marjorie Taylor Greene, the hard-right Georgia Republican, was among the first lawmakers to post false information about the newly released videos. She claimed on the social media site X that surveillance video showed a rioter holding a law enforcement badge in his hand, suggesting that he was an undercover police officer “disguised as a Trump supporter” and the attack was an inside job.

But the item in the man’s hand in the screen grab she circulated appears, upon closer inspection, to have been a vape pen. And the man who is seen in that image, Kevin Lyons, was in fact a heating-and-cooling technician — not a police officer — who was later convicted at a public trial of multiple federal charges and sentenced to more than four years in prison.

Ms. Greene later edited her post to remove the false claim, but not before it had spread widely among Trump supporters.

Senator Mike Lee, Republican of Utah, recirculated the same clip and false allegation that the man pictured had flashed a badge, adding that he looked forward to questioning Christopher S. Wray, the F.B.I. director, about the matter.

“How many of these guys are feds?” he asked in a separate post that included video of a violent clash between rioters and the police.

“Heads up,” former Representative Liz Cheney of Wyoming, who was the top Republican on the special House committee that investigated the Jan. 6 attack, responded to Mr. Lee. “A nutball conspiracy theorist appears to be posting from your account.”

Still others, such as Donald Trump Jr., have shared video of rioters walking through the Capitol hallways doing nothing violent, suggesting that those who entered the building were entirely peaceful. But other videos from that day show some of the same people at other moments storming the building and attacking police officers.

“This is consistent with what they do,” Soumya Dayananda, who served as a senior investigator for the House Jan. 6 committee. “It’s just cherry-picking what they think is going to further their conspiracy theory.”

For Mr. Johnson, beginning to release about 40,000 hours of video footage fulfilled a promise he made to hard-right lawmakers as a way to try to win their support for the speakership. He said that more than 95 percent of the footage — all except parts deemed a security risk — would be posted online in tranches over the next several months.

He strongly suggested that the videos would contradict the public understanding of what happened on Jan. 6, 2021, when hundreds of supporters of President Donald J. Trump violently attacked the Capitol, inspired by his lie of a stolen election, disrupting Congress’s certification of the 2020 election results.

“When bureaucrats and partisan activists withhold data to advance a narrative, it erodes trust in our institutions,” Mr. Johnson posted on social media. “We must restore that trust.”

On Monday, Mr. Johnson sent out a fund-raising email trying to capitalize on the move.

“When I ran for this position, I made a promise to release the footage from Jan. 6, so Americans could see for themselves what happened that day, rather than the opinions of the partisan Jan. 6 Committee,” he wrote. “And I am delivering on that promise.”

News outlets, including The New York Times, had also pushed for release of the videos, to which lawyers for Jan. 6 defendants have long had access. Former Speaker Kevin McCarthy, Republican of California, had allowed the footage to be viewed in person at a House office building, but resisted posting all of it online because of security concerns by the Capitol Police. They have warned that opening the video to widespread public consumption could give future would-be attackers a road map of the Capitol.

The videos show massive crowds assembled at the Capitol, and mobs committing violent acts and assaulting the police. They also show other moments when protesters behaved peacefully while they trespassed through the building, which was closed to the public.

Selective clips focusing on seemingly peaceful moments, and posts using them to cast doubt on what occurred that day, have racked up hundreds of thousands of views across mainstream and alternative social media platforms in recent days.

In one 48-second clip widely shared online — including by Mr. Lee — a detained man appears to fist-bump a police officer after his hands are freed from handcuffs and he is released near a door. The vast majority of posters have cited it as proof that Jan. 6 was an “inside job.” It is unclear exactly what happened in that moment, but officers released many defendants that day because they lacked the manpower to hold and charge the participants. The clip was plucked from a nearly 10-minute file that also shows officers tussling with protesters.

The man in question was later arrested and charged with assaulting police officers.

“The amplification of these narratives by high-profile figures, including public officials, one, gives a sense of validity to these narratives,” said Katherine Keneally, the head of threat analysis and prevention at the Institute for Strategic Dialogue, which has examined Jan. 6-related disinformation. She added: “With this increase in perceived validity, we also have a potential for an increase in threats, especially to public officials.”

Some social media users have used the false claims surrounding the released footage to call for specific members of the Jan. 6 committee to be imprisoned, accusing them of treason.

The Justice Department has charged more than 1,200 people in connection with the attack on the Capitol. The charges show a range of culpability. Some, including the leader of the Oath Keepers militia, have been convicted of seditious conspiracy and sentenced to lengthy prison terms; others have been charged with merely trespassing and received no jail sentence.

“Of course there are people who just followed the crowd and entered the Capitol,” Ms. Dayananda said. “But that doesn’t exonerate the people who stormed Nancy Pelosi’s office, destroyed her property and beat on the cops.”

The videos also show a range of approaches by police officers in different situations. Some fought a bloody battle to keep rioters from breaching the building; some attempted to use persuasion to get people to leave the halls of Congress; others, badly outnumbered, are shown merely monitoring the crowd.

Six Capitol Police officers, out of a force of 2,000, were disciplined for their actions during the Jan. 6 riot, including for unbecoming conduct and failure to comply with directives. But many more fought strenuously to keep the rioters out. About 150 police officers were injured during the assault.

The fact that some F.B.I. informants were in the crowd of tens of thousands has long been known, and it does not suggest the federal government was behind the attack.

Steven M. D’Antuono, the former leader of the F.B.I.’s Washington field office, testified before the House Judiciary Committee in June that he believed there may have been a “handful” of people who had previously served as informants for field offices who were in the crowd that day. But, he said, they had not been asked by the bureau to attend.

The Washington field office “may have had” a drug or violent crime informant in the crowd “that didn’t tell us they were going,” Mr. D’Antuono said, as an example. “People have a citizen’s right to go and protest.”

One of the F.B.I. informants in the crowd on Jan. 6 was James Ehren Knowles, a member of the Proud Boys Kansas City chapter. Right-wing politicians and pundits have sought to spin Mr. Knowles’s presence at the Capitol into a narrative suggesting that the bureau used covert operatives to instigate the riot, but he told a very different story under oath during the Proud Boys’ seditious conspiracy trial.

Mr. Knowles testified that he was not acting “at the direction of the F.B.I.” that day, but had joined the crowd as a member of the far-right group — or what a prosecutor described as “an independent human” making his own decisions.

“You were not there as an agent of the United States government in any formal sense, correct?” the prosecutor asked Mr. Knowles.

“No,” he answered.

Most of the federal informants who have emerged from criminal cases related to Jan. 6 were not tasked by their handlers with spying on right-wing subjects — let alone with seeking to entrap Trump supporters into storming the Capitol. They were mostly far-right figures who were recruited by the F.B.I. to report on their adversaries in the far-left antifa movement.

Attempting to rewrite the history of the Jan. 6 attack on the Capitol has been central to former Mr. Trump’s campaign to reclaim the White House. He has used footage from the Capitol riot at his rallies, suggesting the mob violence was patriotic, and recorded a song with Jan. 6 rioters held in jail.

“Congratulations to Speaker of the House Mike Johnson for having the courage and fortitude to release all of the J6 tapes, which will reveal completely what really happened on January 6,” Mr. Trump said in a video release on Tuesday.

Many Republicans have tried for years to rewrite the history of what happened on Jan. 6, downplaying or outright denying the violence.

One of them, Representative Clay Higgins of Louisiana, last week promoted a conspiracy theory that the federal government had used “ghost buses” to transport undercover agents to the Capitol to carry out the attack.

“These buses are nefarious in nature and were filled with F.B.I. informants dressed as Trump supporters, deployed to our Capitol on Jan. 6,” Mr. Higgins told Mr. Wray at a hearing.

Mr. Wray replied that he had never heard of “ghost buses.”

“If you are asking whether the violence at the Capitol on Jan. 6 was part of some operation orchestrated by F.B.I. sources and/or agents,” Mr. Wray said, “the answer is emphatically no.”