While I understand you’re on the same network when attempting to log in, try the steps outlined in this article, in the “On a Different Network” section:
https://support.plex.tv/articles/200288586-installation/#toc-2
ssh -L 8888:127.0.0.1:32400 username@ip.address.of.server
Browse to ‘127.0.0.1:8888/web’ on your local browser.
Attempting to sign-in from 127.0.0.1 triggers a claim, if the server is unclaimed. Or at least it should.
It worked for me on my FreeBSD 14-STABLE server.
Edit: Corrections so that others seeing this will have correct commands.
