OpenWrt works for some modems pretty fine. It's not straight forward as the VDSL firmware can't often be distributed but poeple use it on avm Fritzbox devices.

OpenWrt works for some modems pretty fine. It's not straight forward as the VDSL firmware can't often be distributed but poeple use it on avm Fritzbox devices. Also LTE devices are supported. Not sure about cable modems, probably not. It's probably involved and not straight forward so for most users, even technical ones it's no alternative.