@AppLee Ok thank you - good to know. I will do that once the bootloader has been unlocked. Maybe the README could be clarified by mentioning that Android 11 and later is not OK?

Edit: BTW, I didn't find a Redmi 9C subsection so the post ended up in a top category.

According to this README, you need to be on the latest Android 10 MIUI FW to install UT.

My device has Android 11 (MIUI 12.5.3), which is obviously an even later version. But do I strictly need Android 10? If so, I suppose I need to downgrade by flashing an older version of the FW?