The same applies to Android OS development. All of it. Android requires a very powerful 1000 USD desktop or laptop computer with 20 gigs of ram and 200 gigs of SSD hard drive space just to compile. This is unacceptable.
Meanwhile, mainline phone linux, like dreemurrs archlinux or postmarketos, can be developed using the same phone it runs on!!!!!!!! All you need is a 20 USD bluetooth keyboard. It is fully awesome. Imagine a world where anybody with just a smartphone and a bluetooth keyboard could be an OS developer!