May I ask what I should look for in the log files to detect this (and so I can configure fail2ban correctly)?

Wait for ninjaCentral to open again and be happy

This is a really great ELI5 explanation of how Usenet filesharing works technically, nice!

Have a look at my German Usenet beginners guide: https://github.com/PCJones/usenet-guide

Let me know if you need any further help

For all German speakers I have a beginners guide: https://github.com/PCJones/usenet-guide

I also use a Hetzner Storagebox for my Jellyfin instance, I mount it via SMB. Works great.

For German stuff there is xrel.to

Usenet is the secret for German stuff. I have a German beginners guide: https://github.com/PCJones/usenet-guide

Thanks, glad to hear I could help :D

sceneNZBs for German content. Will have everything you need :)

If you are using Radarr & Sonarr and want to prefer German DL (Dual Language, German + Original) releases I have a guide for that: https://github.com/PCJones/radarr-sonarr-german-dual-language

Also since it looks like you are new to using the Usenet, I have a German beginners guide: https://github.com/PCJones/usenet-guide/