You should never be required to use your ISP provided all-in-one/router/modem box thing. You can always switch to a decent modem (Motorola makes decent/cheap ones for residential network at the speeds you will likely need), and put your own route behind it. As far as what your ISP can control/see they are limited to the interface device between your network and their network. If you intentionally make it a brain-dead modem then they cant see your router at all and your free to do what ever you want with no oversight.

Why would you be forced to use your ISP router? Anyways, you can probably configure that. Look up the model, find out the login URL and default user/pass, and see if you can log in and make changes.

Was using pihole.

Repurposed pihole as Batoceta retro gaming station.

Set my router to use Ad-guard (others are NextDNS, RethinkDNS, cloudflare DNS family, mullvad).