In the near future I often use the flixbus, sometimes traveling 20 hours. As I still have to do some schooling, I'm about to rent a laptop. To the question: do you have experience with how much inches you can put the laptop on the shelf from the front seat and still work comfortably?
or does not work and you have to balance the laptop on the lap?
So 20-hour trips in the Flixbus are hell.
The rides I made you did not have a table, my longest trip was almost 8 hours and never again.
More than 4 hours is too exhausting, because cramped and uncomfortable, the toilets should not be used and you can hardly move when it is full.
So, laptop is on your lap all the time. Can of course on such extremely long distances other bus models, with tables.
I'm not really helping you, just my experience.