It’s possible for a certain hardware/software setup not to support a certain codec. For example, my jellyfin client (Finamp) uses the iOS native decoders (afaik), which means opus files are practically broken. My music library (8000+ songs) contained exactly 1 lossy file, which just so happened to be an opus file. I decided to spend the extra ~20MB to standardise my entire library to flac files, ensuring I could play every song on all my devices.

Edit cause I posted too soon: you are generally correct; only in very specific circumstances will you encounter compatibility issues like this one in the modern world. This is 100% apple being apple, and you can expect pretty much every other (reasonably modern) device to support all codecs you might encounter in the wild.

To add to the audio compression: it isn’t possible to further compress an mp3 file without losing any quality. You can either:

1. Recompress to a lossy codec (mp3, aac, opus). This will lead to smaller file sizes if you set the bitrate lower than that of the input file, but it will always worsen the quality, no matter the bitrate.
2. Recompress to a lossless format (flac easily being the best one). Going from a lossy to a lossless format will increase the file size (sometimes by quite a substantial amount), while keeping the same quality. There is very little reason for you to do this
3. keep the original files (my recommendation)

If you’re willing to spend some extra time learning about audio compression, you can download lossless files and compress those directly to whatever format and bitrate you want. The quality will be better than option 1 above, as the audio is only lossely compressed once instead of twice.

Have you tried the official guide from the jellyfin website?

As for the guide this AI generated: it bothers me that they instruct you to use chocolatey for the *arrs, but still advice you to install docker, qbittorrent and jellyfin manually (all of which have chocolatey packages). I disagree with the comment that external storage would be recommended, as internal storage is generally more reliable (depending on a lot of factors of course). Also, I believe the “adding a library”-section of the jellyfin setup is a bit too short to be of any use, and would recommend referring to the jellyfin docs instead.

This guide also doesn’t explain how to make jellyfin accessible outside of your LAN. Once again, I’d recommend referring to the jellyfin docs if you want to do this.

I personally have only set up qbittorrent, jellyfin and docker (not the *arr suite), so I can’t comment on the completeness of the guide, but I wouldn’t trust it too much (seeing the previous oversights).

And finally, as someone who started their selfhosted server journey on windows: don’t. There is a reason why almost all guides are written for linux, as it is (in my humble opinion) vastly superior for server usage once you get used to it.

If the installer is small enough (<650MB I believe), you can upload it to virustotal.com to have it be scanned by ~65 antivirus programs