Jellyseerr config/data directory were changed, after upgrading to NixOS 25.05 Jellyseerr will looks like a fresh install asking you to configure it.
Here is how to restore your data, run the following commands as root on your server:
# stop the service
systemctl stop jellyseerr.service
# move the newly created config dir (you can delete config-bk later)
mv /var/lib/jellyseerr/config /var/lib/jellyseerr/config-bk
# create a new config dir
sudo -u jellyseerr mkdir /var/lib/jellyseerr/config
# move your data
mv /var/lib/jellyseerr/db /var/lib/jellyseerr/config/
mv /var/lib/jellyseerr/logs /var/lib/jellyseerr/config/
mv /var/lib/jellyseerr/settings.json /var/lib/jellyseerr/config/
# start the service, everything should be back
systemctl start jellyseerr.service