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

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

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

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/

Just having a Jellyfin instance for family and friends. I have everything in h264 for maximum compatibility to avoid transcoding. All 12 seasons of Bones (2005) take up 800GB alone for example. A 1080P Remux movie takes 10-40GB

Really depends on your usage. I have a few Terrabytes of Usenet traffic every month so I'm glad I don't have to use block accounts for that

If you are looking for German (or German + English dual language) content it can be very hard to find stuff on public torrent trackers and it's pretty hard to get onto private German trackers - but don't worry, there is a solution:

Usenet and the indexer sceneNZBs.com that specialises in German releases have got you covered!

If you want to automate the search for German Dual Language content using Radarr/Sonarr I made a guide (that also works for torrents too): https://github.com/PCJones/radarr-sonarr-german-dual-language

Short answer: no

Long answer: yes, but they are basically useless. Except for some indexers that cost money but also have a free plan where you are capped at like 5 downloads per day.

It's the same, it just adds support for jellyfin

The provider is there to access the usenet, just like you pay your internet provider to access the internet (well, not exactly like that in a technical sense, but you get what I mean I hope). And yes, while there are some free indexers they are basically useless - so you do have to pay for both, usenet access and an indexer. It should still be cheaper than a seedbox though.

To start I’d recommend frugal Usenet for 40$ a year if you are mostly downloading new stuff:

https://billing.frugalusenet.com/signup/neQeZxl

If you are also downloading a lot of older (think 10+ years) stuff you should get ewaka for 48€/year (or keep an eye out for the 36€ year deal that pops up a few times per year):

https://www.eweka.nl/en/landing/special-deal

Let me know if you need more help :)

edit: good indexers to start are NZBgeek (open registration) or Drunkenslug (closed registration, but there are a lot of invites going around). Both cost 15-20€ per year

They are obfuscated and encoded so it's not easy to find the files. Since they are encoded they basically look like random noise instead of actual video files (very simplified)

Looks like first and foremost you need a good(that means paid) indexer. NZBgeek and Drunkenslug come to mind as a good start - they both cost 15-20€/year. Drunkenslug registrations are closed right now but there are a lot of invites floating around. NZBgeeks registration is open.