If I did enable "tofu" that was not on purpose and I would not know how. What are tofu related questions? Is there a doc you can point me to? (Also is tofu.db an annoyance, and if so in which way?)

Hello,
I just hit the same issue in Ubuntu 18.04.5 LTS with gpg version 2.2.4-1ubuntu1.4 and the command line provided on post https://dev.gnupg.org/T3972#127356 by dkg has helped me fix it.
The faulty key was from the Tor project.