I honestly think that any president would be right to questions the results, loudly and openly, if it was an election like that one. That was an unprecedented election. Never in history have we had that much non-traditional voting.
You won’t like this answer but if a president questioned an old time election- vote in person, show an id, results by midnight- I think that would be alarming. But questioning 2020? I think anybody would.
What you’re asking, put another way, is whether anybody should ever question anything that seems fraudulent. Should they just accept something that smells of fraud, because the media (in bed with the winning party) says that they must?