I think what Damian is trying to say is that the modems are now running 802.11ax by default. In theory, devices designed to see older protocols (e.g., 802.11g) should recognize it, however some aren't even recognizing there's even an available wifi channel.
Try logging into your wifi settings: (http://192.168.42.1/wireless_main.htm?t=1707568432118) and changing the protocol for the wifi band that you're trying to use from 11ax to either 11g, 11n, or 11ac (whatever you were using before) and see if it now works.