Dave, did you ever get TPM working on your P51?
I have the same exact model of P51 (20HHCTO1WW) and I love it. It's loaded up with 32GB RAM and 1TB NVMe SSD. But I was hoping to use it with Qubes and TPM.
I'm a firmware developer myself, though so far not on PCs yet. I'm wondering if integrating support for TPM 2.0 is beyond my ability or more a matter of the very capable core maintainers being occupied with higher-priority stuff. If it's the latter, perhaps I could try it...