The roombas with cameras don't need an internet connection to work-- they need it if you want the app control features like scheduling. The imagery based navigation is still local.

When I got one in ~2019, I covered the camera and connected it long enough for it to get firmware updates (which annoyingly you can't trigger and it takes a few days)... then I firewalled it off to get no internet access.

I later figured out that if you let it connect and firewall it off it just sits in a tight loop trying to connect again hundreds of times per second which meaningfully depletes the battery faster.

Changing the SSID name so it couldn't connect to the wifi solved the problem.

I'd like to get a new one-- the old one still runs well (with some maintenance, of course) but the latest robot vacuums are obviously better. Unfortunately at least some are more cloud dependent and I can't tell which are and to what degree.