completes without error. Search by name at openpgp webgui fails, but search by key id via web gui succeeds. Search by both keyid and name via android app (openkeychain) fails.
ETA 2: Ubuntu server works fine. Guess something is up with openpgp.
Yes, this is maybe an issue with keys.openpgp, have you asked there?
Note that the tutorial is from 2022 and in the years afterwards a new decentralized network of public keyservers has established itself. They sync keys with each other.
I personally recommend to use the web key directory if you can and then one of the decentralized, non-validating keyserver that are in the network, see SKS Peer Mesh.
Ubuntus server sometimes does not sync with that network and keys.openpgp.org is too centralized and validating for my taste.