I’ve been working on the same thing with the 6.4 kernel where it is suppose to be enabled by default but alas i’m getting the same as you - some SBIOS _CPC flag not on the cpu feature extensions. I"m running the TRX40-Prime Pro with a 3960X.
I have gotten this to work on my laptop 5900HS full ACPI suppose since there were patches - So 5.something kernel.
My guess is with others - its not been enabled in the bios. I have still been updating mine as recent as the last couple months.