I curently have 8.5 on an imac and 2019.(2?) on a PC. They share projects via Mimic, and i routinely open them on each others computers, and (sometimes) at the same time.
Only caveat is that my PC is symphony and the imac is more basic, so any outputs (prores) that i might want to do out of the imac may have to go through a video mixdown in PC box first…if there is any symphony color effects being used in the timeline.
But from a purely open the timelines, play them, edit them close them, open them on the other box it works fine.
I think there might be an issue if you try to go prior to v7 or 6…but you should always be able to export aafs back and forth with little issues even on older systems.
Glenn