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

Korean war and probably Kosovo war (or Yugoslavia wars in general) for Serbia

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

Unironic communists using ml as short form of marxist-leninist.

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.