Why would you expect peaceful protests to work in that scenario though?

The point of peaceful protests usually is to say "hey, look at all these people who are going to vote out candidates who don't do what we want and vote in candidates that do what we want". But if voting itself is rigged, then that is not a proper threat.

Trump supporters already had multiple peaceful "stop the steal" type protests prior to the 6th and showed up in large numbers to Trump rallies that happened after election day.

Every peaceful protest has this implicit underlying threat, and it is part of why peaceful protests work. "Look at all of the people who will be pissed off and might cause disruption or do something violent if you don't listen to them".

If the first threat (voting people out) is not a serious threat anymore, then we are only left with the second threat as leverage. Now, there are ways to cause disruption without violence and that is more moral. Examples would be a refusal to work or pay taxes in masse. But it would be very difficult to get enough people to participate. People felt that it was very urgent to save the republic and that is why some were motivated to take more drastic actions.

Keep in mind, most of the people who stormed the capitol were engaging in an act of non-violent civil disobedience. There were people at the front who fought with police but the vast majority of the people who went in just walked in after the police had already stood down or retreated further into the building.