Some of these "stolen" elections took place under Republican state administrations, supervised by Republican appointed election officials. WTF are these people doing if tens of thousands of votes are sneaking through the system and they can't find any evidence of it, and say themselves the election was fair?
Trump did exactly the same thing in 2016, claiming massive vote fraud and that the election was being stolen from him. Not only did he provide no evidence, but his own Justice department and subsequent administration was unable to find any evidence. If he really though the electoral system was so badly flawed, he had control of the House and Senate to do something about it, so why no voting reforms? If he actually believed his claims why didn't do something about it?
The truth is he didn't do anything because there's nothing to be done. He and his people know perfectly well the electoral system is fair, that's why they haven't bothered to reform it. There would be no point. In fact it would simply make them responsible for the voting system and thus unable to claim fraud anymore. Instead he's simply using claims of fraud as a tool to incite his supporters and avoid the ignominy of being a "loser". Something he has said many times he cannot tolerate.
Both his words and his actions show very clearly this is a pre-meditated attempt to undermine democracy in America.