I have used AdGuard for years and it works great.
https://apps.apple.com/us/app/adguard-for-safari/id1440147259?mt=12

Yeah its unreliable. Its probably the dog.

Anything is possible. If you notice problems with it afterwards then yes you damaged it.

congratulations?

If the app developer uses their own sound then they will continue to. If they use the default sound then no you cannot change it.
https://9to5mac.com/2023/09/19/ios-17-iphone-app-notification-sound/

nope.

no major problems, it’s fine.

Apple Support answers this here: https://support.apple.com/en-us/HT201302

Tap it, open the app, and find out.

You can sell anything to anyone if they are willing to buy it. (not legal advice)