Yeah im in the US. I use Tmobile and it works fine for me, 5G and all. Looking at the bands that the POCO F5 supported, it seemed like only Tmoblie uses one of the radio frequencies that the F5 uses for 5G. That probably means that I wont have 5G everywhere in the country, but I lucked out and its good for where I live.
With MIUI, i did not have the option of Wifi calling with Tmobile, for some reason, but on Paranoid Android it works just fine.
IIRC the F5 had more bands that worked with Tmobile and AT&T for LTE
Edit: This was when I bought it. Carrier band support may have changed since Nov 2023