xcompat/doc/gameid.md

GameId API

minetest versions >= 5.7

simply returns minetest.get_game_info().id

minetest versions < 5.7

approximates the gameid value via a hardcoded table of gameid => modname, and then checks via minetest.get_modpath(). If it fails, it falls back to using xcompat_unknown_gameid as the id. See the chart in the readme for which games are supported