Just a note, according to all major sources, Biden won by 7,060,140 votes total. Not saying those 400k deaths may not have influenced certain key swing districts. But there was definitely a much larger gap than 'thousands'.
That's in terms of nationwide total vote count. That's not how the electoral college works though. Biden won by a few thousand votes in a few key swing states. Therefore, it is more accurate to say that Biden won by a few thousand votes.