I have plenty drm free games in steam where I copied the game folder into other computers and it ran offline. At that point, there’s no difference between an installer and a compressed copy of that game. For reference, Grim dawn but there’s plenty more.

“Installing” is just semantics for decompressing a file in specific folders, you can the collect that data and “install” the game wherever. As long as you can run the game without steam, it doesn’t matter that you used steam to buy it.