Here's another logistics issue with Trump fleeing: The Secret Service. They don't work "for Trump", and would be obligated to report any attempts by Trump to flee.
Sure a former President can waive SS protection, as Nixon did, but I imagine the process is a bit more complex than Trump just telling his SS detail to go home. And if Trump did try to weasel out of having SS detail that would set off alarms and I have little doubt there'd be other law enforcement surveillance of him.
He probably only flees if people decide they want to let him. But if, say, NYS orders him to report for imprisonment during the Campaign and he announces a tour of Europe, the Middle East or South America at the invitation of local governments? Does Biden block him from going?
You are correct however. The Secret Service aspect means this is unique because there will come a point where Biden and his team will have to make a policy decision about how they want this to go. At the very least because no one lower is going to want to take the fall for it in the event things go badly.
I mean that's all out the window if you think Trump would voluntarily serve time but nothing in his history makes it likely he would chose that path over maximizing the damage inflicted on Biden and the country. At the very least I am certain he will try and screw over DeSantis by forcing him to either block the arrest or take the fall for failing to do so.
Trump under house arrest in Palm Beach is the best option for most actors, but it requires a lot of people, including Trump to play along.