To create a linux distribution under your own control you don’t even need to engineer anything new. You need to create deployment structures but the tools for repository hosting, package managers, build services, automation and pki are already there. It’s more about curating software and sometimes auditing or changing code. Someone who’s capable of reverse engineering Blu-ray player firmware should be able to learn this as well.

Edit: ‘A new distro’ is also a spectrum. It’s a big reach from creating a debian distro with some version differences to something like openwrt or asahi linux