Can I verify that 5G home internet router is sending a full 2.4G signal

Just started with 5G home internet. Everything worked great until I tried to use our old wireless printer, which only supports 2.4G. There is just enough of a signal for the printer to find it and verify the wifi password, but the signal is not good enough to do any real work, and the printer refuses to connect. After an hour and a half of waiting on hold and being told that an "expert" would solve my problems, T-Mobile "support" blamed the printer.

So I did a bit of research on routers and learned that dual band routers, which support 5G and 2.4G, frequently have the 2.4G band turned off to enhance 5G performance. I'm wondering if that happened to my router (or actually that the signal is weakened in my case). I can't find any documentation on the so-called gateway or any interface to activate both bands or even query the status.

Any suggestions would be appreciated.

Houyhnhnm