Further, at least in this election, voting and registering to vote were one in the same in many jurisdictions. Many states automatically sent out mail-in ballots to everyone that was registered. All that had to be done from there was to fill it out and send it in. Families of dead people sent in those ballots in many cases.
Registering to vote as someone else, or as an entirely fictional person, is absurdly easy in many jurisdictions. In California, for instance, one can skip any identity checks by simply marking two checkboxes: one indicating they have no ID, and one indicating they have no social security number [1]. Voila, you are now a registered voter. Combine this absurdity with automatically sent out mail-in ballots in many states, and you have a disaster waiting to happen.
You claim fraud and offer a video as proof. The video contradicts you. In it they explicitly say, a few times, there wasn't any fraud.