I finally got the CPU clock unlocked last night, it required setting `intel_pstate=disable` along with some other kernel params and a write to the MSR.

as best I can recall, disabling the intel_pstate driver wasn't required on Debian 12, some changes to the driver since then have prevented overwriting the no_turbo flag in certain cases even with root privileges.

I ran probably a couple dozen web searches related to this, and found some forum posts and kernel bug reports and mailing list posts which lead me to believe that this may in fact be a bug, and thus likely to be fixed in future kernels, but I can't wait around for that, so falling back to the old ACPI frequency scaling driver will have to suffice.