We had Comcast for 17 years, and they always allowed us to bring not only our own router, but our own modem. Even when we rented a combined modem+firewall+AP from them, it was trivial (and documented) to put it into bridge mode.

We just switched to Metronet last month (5gbps symmetrical!), and while we have to pay $10/month to get a public static IP (CGNAT otherwise), they didn't care what was connected to the ONT, which operates below the IP layer.