This question has already been asked and answered for the more expensive device:

Here is the answer from Alain Elgamal (digitec):

"Alain Elgamal
5 months ago

All Xiaomi 12 models are 5G capable, unfortunately the titles are irritating, sorry.
There are only differences in the colour, in the size of the RAM (8 GB or 12 GB) and the storage space (128 GB or 256 GB). Because we obtain the data sets from different suppliers, they are unfortunately sometimes incomplete or errors can creep in. However, we do our best to constantly optimise the data sets."

Xiaomi 12 5G is 5G capable according to the settings - what both settings actually change I cannot understand - the blood-brain barrier opens 4G anyway!

One is 5G-capable, therefore also not cheaper

I don't know