Get One UI on any Android with Ancient OS 5.4 Custom ROM - xiaomiui
This is Noble rom, an android 12 custom rom for the Galaxy Note 9 and S9 by AlexisXDA on XDA. It has some bugs but nothing that's deal breaker, some stuff have
How to Install Custom ROM on Xiaomi Redmi Note 9 S/Pro/Pro Max and POCO M2 Pro | Medium