With Linux 99% of the time you should use the software repository or “store” or “Discover”. You’ll get the latest supported version on your Linux, it takes care of updating, and in my experience it’s worlds more reliable than Windows store. Also poke around and see what’s available; it’s all free software and should be perfectly safe.
It looks like you can still use it strictly for modem duties and use your existing router. That’s what I do (albeit with AT&T fiber), and the only downsides are you have to port forward on both the “modem”/C5500XK and your router, and things like dynamic DNS is potentially more complicated to setup.