so Trump can still be president in 2021 +?

https://www.youtube.com/watch?v=WZWRhLW7Y8w
What if a US presidential candidate refuses to concede after an election? | Van Jones

start at 7:43

Concession is a purely symbolic gesture. If you don't concede you don't get to just veto your successor.

Trump flailed around during election night and subsequent counts, he's flailing around in courts, he will flail around when the electors meet and vote, he will flail when the senate counts the votes, he will flail around when Biden's inaugurated.

And he is going to flail around and cry when Biden's inauguration crowd is bigger than his.

yes, there are no rules against ex-convicts running for office. That only applies to being elegible to vote.