You can. But it then has to route through their modem+router single piece unit.
E.g. I have my own router which handles everything I need. But I switched ISPs recently to save 70$ per month, and the new company router has parts of its functionality, like turning off the wifi, built into their smartphone app and disabled in the admin panel.
Also the username and password for the unit is, by default, admin/admin. In 2023.