S33 is just a plug and play device you can connect modem to power and coax then activate modem by your ISP internet service provider you can then for activation or you can do self activation on Xfinity app.

 https://www.xfinity.com/support/articles/xfinity-app-activation

Xfinity says they can't see modem. This is second brand new S33 in a row that can't be seen, even though cable signal checks out to the connector and the light is solid blue on the modem.

Could you let us know whether the modem is connected to the router or directly connected to the computer through hard wiring?

Also, I suggest checking the IPV4 address through a direct connection.