If there was an election fraud, Trump would not have become president in 2016 to begin with, when he also claimed that the system was rigged. And why would Republican controlled swing states admit their own party's defeat if their candidate won? My own country also sent election inspectors, which did not see any intentional fraud, just the standard mistakes in counting ending up in favor of either side. When an election is rigged, it's usually in favor of the incumbent leadership, not the outsiders. The only way to cheat in the US election, is by openly gerrymandering election laws, which Trump openly supported.
Believing in Trump's fraud claim is more like saying that Elvis is still alive, because accepting defeat goes against the core principles of Trumpism.