Buy your own DOCSIS modem, opt out of renting theirs. It'll pay for itself after a few billing cycles (the modem rental fee is $15 per month)

I bought a DOCSIS modem+wifi AP on amazon a decade ago for $50. Its been working like a champ and I have control over it.

although for the best control it is recommended to buy modem separately and wifi AP separately, because Comcast can send C&C commands to your modem over the copper cable