Trump actually outlines that in the speech before the riot, although he does it in such a meandering Trump-y way that it's hard to parse. He wanted Pence to send it back to the states to have a better look at things, although that would have been messy as hell.
"So as an example, in Pennsylvania, or whatever, you have a Republican legislature, you have a Democrat mayor, and you have a lot of Democrats all over the place. They go to the legislature. The legislature laughs at them, says we're not going to do that. They say, thank you very much and they go and make the changes themselves, they do it anyway. And that's totally illegal. That's totally illegal. You can't do that.
In Pennsylvania, the Democrat secretary of state and the Democrat state Supreme Court justices illegally abolished the signature verification requirements just 11 days prior to the election."
"More than 10,000 votes in Pennsylvania were illegally counted, even though they were received after Election Day. In other words, they were received after Election Day. Let's count them anyway."
There's a ton more. Some true, some not, etc. The annoying part is the media completely disregarded stuff like this, which only enraged his base more.
The real issue in my opinion that we don't have enough systems and transparency in place to be 100% sure our elections are fair. We should have random audits.
Hijinks with what same states pulled with their election laws during COVID shouldn't happen. Hillary Clinton claimed Trump stole the election from her, so this isn't a new feeling - Trump just had an actual support base he could rile up. Unfortunately for all of us, with the political system being so partisan I fear nobody can even propose more election security without coming off like a crazy person.