We need to stop calling it digital "ownership"! You don't get to own anything as a customer on these platforms, because rights that can be taken away on a whim are no rights at all.
In the case of pc platforms like GOG, and itchio, if you get a drm free version of a title, theres nothing the company can do to both stop you from storing it on an external storage (or multiple) if you wanted. They wouldnt be able to revoke it if its a single player game.
GoG about page explicitly talks about owning, and terms even explicitly mention advance notification so you can download Dr free versions if they will ever become unavailable.
GoG terms do not qualify purchases as temporary access licenses - only to the degree of servicing downloads as long as possible and without other limitation.
We don't believe in controlling you and your games. Here, you won't be locked out of titles you paid for, or constantly asked to prove you own them - this is DRM-free gaming.
What you're talking about is being allowed to use something or being tolerated, that's different from having a right. A temporary right is a real right for a specified time frame, but here it would just be "until I decide you don't".