Often it's not the phone that is the limitation, it's the carrier settings. Those can be set by the device, the SIM card (or eSIM) or the carrier itself. I don't know anything about Xiaomi devices, but I know on the Samsung Galaxy S models I have (S22, and S24U) it's quite easy to modify the channels allowed with a little hacking. I'm not sure how many markets in Europe have true 5G SA. I was surprise to see that there are still many places that are only 3G (or even 2G) when I was there last year. 3G networks were shutdown in most of the US 4-5 years ago, and 2G about 10 years ago. Don't get too hung up on what mmWave bands are supported. mmWave has pretty much been a failure so far (for phones). mmWave requires mine of sight, which isn't (yet) realistic with moving devices. C (or Mid) band is where it's at for speed these days.

I run my own private 5G (SA) cellular network. I need a minimum iPhone 13 or Galaxy S22 to support n48 (CBRS). I prefer Android devices because it's quite easy to adjust and debug carrier settings. Apple would never allow that on their KindergartenOS.