As far as I know this model, Xiaomi 12S Pro is a phone for Chinese market. If my guessing is correct, then could be an incompatibility between internal modem and the network.
Also check the coverage and what bands (frequencies) are used by your mobile provider on the area where are you living.
As a quick check, take a look on this page about your phone compatibility with Hungarian mobile networks:
https://www.kimovil.com/en/frequency-checker/HU/xiaomi-12s-pro