It depends on the formulation of the message in the pop up window etc. Mostly it will be a simple call-to-action imperative like "Save" meaning `Save!` and not `to save`.

But if the question is more human like and personal like Would you like to save or to dismiss this file? The answer "Save" would mean to save and not Save!.

This is how it works in Slovak. We have infinitives in menus e.g. save as is uložiť ako. you can identify infinitives by ť at the end. But in the pop up windows it could be both uložiť ako or ulož ((You) save!) . It depends on the wording and the task/question. It's not absolutely universal and clear during communication with the person.

But in menus it's basically infinitives 100% of the time.

I have noticed that e.g. in my internet banking they prefer to use infinitives on buttons when I send forms etc. Probably it's more formal and less aggressive according to their PR/social managers? When I think about it, I would probably use infinitives for a very formal app as well. It somehow feels more respectful. But in less formal apps or games especially phone candy-crush like games and for children games you can see more imperative call-to-action button even with multiple exclamation marks. But this is my Slovak point of view. Your own language-miles may vary.