Apple

It’s a bit complicated to reply as in your hypothetical scenario we literally have no information. It’s like me asking “if I’m sick, will I die?” Well it depends… do I have final stage cancer or a random cold? That’s assuming there are viruses in the first place, which iirc they exist but are extremely rare

It depends on how it’s integrated into the system. Restoring from a backup (just downloads app data and settings stuff from the old device so I doubt it would transfer anything.

That depends. Hypothetically, you could only get a virus from jailbreaking your phone and side loading apps. A jailbreak wouldn’t transfer to a new phone, and those malicious side loaded apps wouldn’t either. In theory, your transferred settings are just non-executable configs that get copied, and you redownload your App Store apps direct from Apple. But, hypothetically, if the exploit was in an app that made its way into the App Store, or a vulnerability within iOS itself, or part of a transferred config file that is somehow also executable, then the virus could potentially transfer. But since we’re all hypothetical here I’d say no, by why risk it? If you knew you had a malfunctioning iPhone or had jail broken it, set the new one up fresh.

Hypothetically, possibly. BUT why not start fresh to ensure you're free from viruses Hypothetically.