I can’t imagine it’s due to updating to v12.9.0 but, cutting the power for at least 10 minutes (not 1) solved the weirdest after update issues.
But to me this sounds like the IPv6 bug.
If possible:
I’ve 2 Pro 2019’s, v12.9.0 and did not experience the “not installed/installable apps” bug (ever).
And I (de-)install apps almost on a daily basis.
