Linux is commonly used in the communications systems, like on invidual radio “stations”. Propably used everywhere where high confidentiality and security is required.

Real shame that GrapheneOS only supports google pixels since they are kinda expensive.

Yes, though there are some prebuilt binaries for large packages. I use gentoo on a desktop and updates don’t take too long, minutes. Big updates that cause lot of packages to rebuild can take hours.

There is fine line with being tech illiterate and being able to use linux when it all just works. The problems arise only when you are just slightly more advanced and want to do something weird without actually being able do it in linux with some things being a bit too much for the average Joe.