No Python 3.9 installation was detected

Attempting to update from 3.8.6 x64 to 3.9 I get the above error. I click OK, it comes up again. I click OK again and I get 0x80070643 Fatal error during installation. I’ve tried a clean install, no issue, but 3.8.6 re-installs with no problem. I’ve tried disabling malwarebytes, and running the net framework repair tool, both to no improvement.

Running Win 10 Pro x64 1909 18363.1139.

Log at:

Any idea why this may be happening, and how to resolve it?