For the last two you do have limited sideloading via things like Altstore, the catch is that without a developer account you have to refresh the apps once a week or they can’t be opened anymore, and you can only do it for three apps at a time (including the altstore app).
There are other ways but that’s the only one I know without jailbreaking.
Back when I had an iPhone I always had an emulator and a third party YouTube app sideloaded