The difference isn't a loophole.
There is no loophole that allows people to temporarily steal things as long as they kindly return them later.
See the model penal code[1] "(1) "deprive" means: (a) to withhold property of another permanently or for so extended a period as to appropriate a major portion of its economic value, or with intent to restore only upon payment of reward or other compensation"
See [2] which mentions the "permanent" requirement three times.
[1] https://archive.org/details/ModelPenalCode_ALI/page/n207/mod...
[2] https://www.findlaw.com/criminal/criminal-charges/theft-over...
To clarify, most jurisdictions have definitions of theft that will be true even if you only deprive the person of their property for a short period of time:
> Today, many states have extended the definition of theft to include depriving the owner of the property even for a short period of time, thus rendering unauthorized borrowing as theft.
From https://lawshelf.com/shortvideoscontentview/theft-crimes-a-s...
So yes, maybe there is some jurisdiction somewhere that wouldn’t define unauthorized borrowing as theft, but chances are good that if you borrow something without authorization, you can be guilty of theft (among other things) in most jurisdictions.
Theft generally (specific statutes may vary!) requires intent to permanently deprive; if you don’t have that, its not theft.
It may be another crime, and its almost certainly the tort of trespass to chattels, so its not “allowed”.
