Generally it’s fine, but right now, with my laptop, I’m having to use run an older kernel version because the Nvidia drivers haven’t been updated in the Ubuntu repositories. Installing drivers for Nvidia isn’t hard, but it is something you have to elect to do, and it is something that can break. Meanwhile, with AMD GPUs, it generally ‘just works’.

IMO, given two laptops of equal value, I would pick the AMD, but I wouldn’t pick a worse laptop in order to have an AMD card.

You’ll have to ask them. Maybe you should, and maybe they’ll consider it. If you don’t ask, it’s much less likely they’ll think of it themselves.

Because properly packaging/distributing your game is hard. Maintaining a build environment, running tests, having unique deliverables, it all adds effort. With Proton specifically, it’s a much lower effort to report. If there is a linux specific bug, it’s fine, because Linux isn’t officially supported, it’s just known to work with Proton. You also only need to ship one binary file (the Windows build), so you don’t have to adjust or alter any processes.

This may not be the reason they do it, but there are real reasons.