Can’t always do that. At my last place I had att fiber with an all-in-one modem/router combo. You could not opt out and use your own modem. Best you can do is use the all in one as a pass through to your own router

Tangentially related: I have a 2022 Subaru, I used to have a 2021 Subaru. Subaru has a mobile app where I can start the car, locate it, unlock the doors, etc. When I traded in the 2021, it never removed it from my app. I’m able to see where the car is parked, and presumably start it, open the doors, whatever.

I tried contacting Subaru, I looked for a bug reporting or bug bounty but couldn’t find one anywhere. All I could find was instructions to remove the car off of my app. I view this as a huge privacy breach, it shouldn’t be my responsibility to remove the previous owners info from the app.