I think that Biden ballot-harvested his way to victory and Trump never put up a coherent argument against it.
I definitely think there was shennaigans when i went to bed at 3 am hearing that states were done counting - only to check back in at 5 am to see mysterious dumps in Wisconsin for Biden (guess they weren't done counting woopsies!).
But to your point, i don't think Trump ever presented anything that a court could use to overturn the election.