Device name:Xiaomi 13 Ultra
Codename:ishtar
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 13 Ultra(ishtar) - MIUI Official ROMs