This is an odd bit of political trivia but enough of the states which Trump won his electoral votes from have laws forbidding Felons from taking office. If the democratic party just sues in those state, they could revoke enough electoral votes to prevent Trump from getting his second term.
It just requires them to enforce the laws that already exist. The only counter the Republicans have is to repeal the laws preventing felons from holding office. (Some of them started to realize this https://www.latintimes.com/republican-bill-inspired-trump-would-let-convicted-felons-run-public-office-missouri-568981)
The Supreme course case you provided is a very good point to make.
I think what OP meant however was more of invalidating the electoral votes that went to Trump in those states. This would remove a significant number of votes and potentially put him below the 270 mark. I don’t think it’ll work out because like you said, Trump stacked the Supreme Court in his favor last time around. Any challenges will be shut down by them.
But on what basis would the states be able to invalidate those electoral votes? From the federal perspective, Trump is eligible to serve another term as POTUS, even with the felonies and treason. A state does not have the authority to invalidate those electoral votes based on state policy, as outlined in the Supreme Court case from March, so the situation would apply here as well.
What it then boils down to at that point is whether or not a state in question permits faithless electors, which some do but the majority do not.