This is just false. As sibling comment mentioned Valve doesn't do third party exclusivity, but also the Steam DRM is completely optional and there are many game

This is just false. As sibling comment mentioned Valve doesn't do third party exclusivity, but also the Steam DRM is completely optional and there are many games for which Steam just acts as a downloader and automatic update system. You can just copy these games' folder to another PC and run them without issue.