Device name：Xiaomi 12S Ultra

Codename：thor

Bootloader：You need to unlock the bootloader if you want to flash a rom into your phone via fastboot method, and your data could be deleted as you choose, please make sure you have backed up your personal data. , Apply for Bootloader Unlock here.

MIUI Roms：Yes , go to the MIUI site: Xiaomi 12S Ultra(thor) - MIUI Official ROMs