The reverse of that is likely just as true; people that are happy Biden won, have no concern if there was fraud, just like those that wanted Trump to win would not question him winning.
You're probably right. I'm not a fan of Trump, and I'm not sure how I'd feel if I found out that there was truly fraud and the election belonged to Trump.
But I am in favor of investigating all (legitimate) allegations of fraud, not just the ones that DJT wants to investigate. And counting all ballots.
This is probably the new normal. Republicans have learned a thing or two of after four years of claims about Russia stealing the election. Both sides will work overtime now to delegitimize winners whenever possible.