One of the requirements is full secureboot and recovery arrangements that didn't exist when I installed back in the 8 days. Now I can reinstall over the old drive and that will do all the plumbing that enables 11. So the hardware is 11 compatible, but the existing software install isn't.

*Edit to answer the question, no, it's not too late. Most compatible CPUs have a lesser firmware TPM, but most mobos have a slot for a vendor specific hardware TPM. Which is what I got.