False, it's not what is done ever since Al Gore contested the 2000 election.
John Kerry called Bush the day after the election and conceded.
John McCain, no problem.
Mitt Romney, no problem.
Hillary Clinton also conceded to losing the election right away and attended the inauguration as well. She might have dropped some hints about questions here and there since, but that was to sell a book. Not to mention, everybody was asking those questions. She never contested the election.
The only one who contested the 2016 election was Trump. Yes, Trump. 2016.
And Trump, again, in 2020.
And Trump, again, in 2024. He claimed that the election was rigged. That it would be stolen.
He was telling the truth.