I know getting the actual DOCSIS module working is out of the question, but this modem has a regular
Broadcom BCM49xx soc and people are practically giving away their modems due to them being network locked.
I just opened mine and I see what looks to be like uart pins on the mainboard- is there some specific reason why nobody is pursuing this before I spend more time on it?
The device you linked to has no ethernet WAN option, only 4 ethernet ports on a lan switch - if you can build an image maybe one of the ports can be made a WAN port, or maybe not.
If your plan is to use it as an access point then the factory firmware will do a better job than openwrt can as the wifi6 hardware is unlikely to have any opensource support, if the device is all broadcom.
There are other threads about attempts to create images for cable modem all in ones (search for 'cable modem'), they don't go anywhere as 1) the docsis hardware will never be supported and that's the most interesting part of the device and 2) these tend to be all broadcom devices with limited to zero mainline support.
It's your device so have at it - if you can get a working dts then openwrt should boot, how much functionality you have will depend on the amount of time and effort you want to spend.
Edit: there are two BCM49xxx devices in the TOH, they may help you get started. Neither has Wifi6.
There are two main issues with docsis and these devices:
it's pretty much always Broadcom, which means
no drivers for the cable/ docsis modem
no WLAN drivers
no FXS (analogue phone) drivers
no DECT drivers
for some of these SOCs a weird two-stage bootloader setup, which would require a non-redistributable second stage bootloader in the OpenWrt image
barely anyone who wants to put up with that hardware, investing quite a bit of quality time for the development, given that the best you could achieve, would be a wired-only router, which is rather on the slow side without Broadcom's proprietary acceleration (ctf.ko, no drivers for that either)
docsis modem drivers do need to authenticate themselves to the ISP via certificates, so even if the drivers were available (which they are not), you couldn't use them anyways, as you couldn't get them signed- and accepted by the ISP