Unfortunately, I am far from familiar with what used to be called “modems”. I have been on Fiber Optic for some time and my ISP provides the Optical Network Terminal (aka modem). All I provide is the WiFi Router to plug into it. I have also never dealt with Xfinity.
What you choose will depend on what type of Xfinity service you have (cable or fiber) and what Xfinity allows. If they will provide the Modem and you buy the WiFi router, that is easiest. If you have to buy both seperate, the Modem has to be compatible to their specs. They should have a list of compatible modems. If you are going to get an all in one (modem\Wifi combo), again they will have to confirm compatibility.
If you go with seperate boxes, here is a good discussion about WiFi Routers that work good with Wyze gear. If you have questions about any of them, jump in and ask questions. There is a user in that thread with Xfinity.
I believe the other Mavens may have experience with Xfinity. With your permission, I would like to invite them into this DM so they can weigh in with more helpful info if they have it.