1st Problem, Jellyfin crashing:
After installing jellyfin, I got "(jellyfin)[7589]: jellyfin.service: Referenced but unset environment variable evaluates to an empty string: JELLYFIN_ADDITIONAL_OPTS, JELLYFIN_FFM>" on my Fedora 43 desktop.
After searching I found this, which was edit IsStartupWizardCompleted to false, and it worked, I went ahead with the wizard setup.

2nd Problem, New devices connecting via webui are shown the setup wizard instead of login page:
On my Desktop and TV works fine, but when I try to connect from my laptop, the setup wizard comes up, whether is the web version or the media player version.
With one more search, I found a user with the same problem, and the solution is to change IsStartupWizardCompleted to true, but it does crush jellyfin.

SOLUTION WAS FOUND and was easier than you think
I did clear cookies on my desktop for web jellyfin, server installation came up, went through it again, and now it works fine! I did login without problems on my laptop.
Will monitor and see how it goes.

Looks l