My 12T Pro:
My phone supports two micro sim in its sim tray as well as one e-sim. If you have the same model and same eu firmware one thing that could prevent you from using your e-sim is the region setting. Maybe try germany or some other eu region.
have you tried contact Xiaomi support? This page has live chat or you can submit a ticket - https://www.mi.com/uk/support/after-sales - I used live chat regarding another matter and got through to someone quite quickly - I'm sure they can explain to you about this.
Now you can see on the website that:
"Dual SIM (nano SIM + eSIM and nano SIM + nano SIM)*Use of eSIM requires a wireless service plan. This service plan may be subject to certain restrictions of use on switching service providers and roaming (even after contract expiration). eSIM availability may vary depending on country/region and carrier (https://www.mi.com/global/support/esim). For more details, please contact your carrier for more information. "
I believe that eSIM will be in any device, but because China is not supporting eSIM, they chose two nano SIM.
I need to check with the Europe ROM need to wait seven days to unlock the bootloader.
Better contact support. I use a Xiaomi 12T Pro bought in Germany with EEA firmware (126.96.36.199 SLFEUXM) which has an option in Settings->SIM cards & mobile networks -> Use eSIM. I cannot test this option as I use a standard micro SIM but it should be there according to the EU version of MIUI for the 12T.