Starting with kernel 5.9 (xanmod just updated to 5.9) the user-space writes to MSR are met with a warning (but are still allowed).
If you undervolt your CPU using MSR writes, you will find such warnings in your boot log:
kernel: msr: Write to unrecognized MSR 0x150 by wrmsr
Please report to [email protected]
You can remove these by passing the kernel option msr.allow_writes=on
More info here
I hope this helps.