That is not a plane if you look close. That is thieving. The board layout had no copper there, but this can make the plating process more difficult to get consistent across the board. Usually this is added by the fab house to help them manufacture the board.

It doesn’t usually work that well in practice. I have been running an M1 MBA for the last couple years (asahi Arch and now Asahi Fedora spin). More complex pieces of software typically have build system and dependencies that are not compatible or just make hunting everything down a hassle.

That said there is a ton of software that is available for arm64 on Linux so it’s really not that bad of an experience. And there are usually alternatives available for software that cannot be found.