With Godot you completely own the game! I've tried to go back and update old GMS projects made with a previous version, and opening the game in the current patch of GameMaker will lead to issues and broken projects. Godot Engine is Open Source and every version of the engine is available to download, along with the source code for it. Going back to old Godot projects is easy, like this game Candy Wrapper I ported from 3.2.2 to 4.1. Godot is also completely free and exports to different platforms! I paid $100 for HTML5 Export license in GMS2, Godot is completely free and always will be. Try it out(+;