Linux

Just adding to this for other people that don't know: you can also install most* standard Linux applications and tools on SteamOS, as long as it's available as a Flatpak, or you can install it to your user directory. Technically, you can even bypass that last caveat and install whatever you want, but you're going to have a bad time if you don't know what you're doing.

Alternatively, you can install any Linux distro on your Steam Deck if game dev isn't a good experience for you on SteamOS. In fact, Bazzite is working on a GDX (Game Developer eXperience) edition, and will likely be a solid choice once it's ready.

However, since currently the Godot launcher is bundled together with the Godot Engine version and all that updates together, late in development of a project you'd want to avoid auto updates since it may break your project at unfortunate times by introducing feature incompatibilities though feature depreciation or regression bugs that causes issues for your game.