I think @mark-robustelli is on the right track.

Ensure that you have configured the correct search type.

If you were to remove the configuration file or install into a new directory for the upgrade, you may be picking up the default configuration which will have search.type=database set as the default.

You can change this to search.type=elasticsearch for use with Elasticsearch or OpenSearch, or set an environment variable FUSIONAUTH_SEARCH_TYPE=ELASTICSEARCH.

See search.type in the config reference.

https://fusionauth.io/docs/reference/configuration