Sure, I am not a fan, but I don't see any huge issue with this. Unfortunately, quite a lot of projects do stuff like this. If you are really concerned you can use matrix without using anything from matrix foundation (aside from the protocol) there are alternative clients like cinny. And even alternative servers like conduwuit.
Don't get me wrong, I use Beets for my entire library, but it doesn't solve any of the issue OP has. It does not get metadata from streaming sites or anywhere else, but same as Picard from Musibrainz. It does not allow to manually change metadata of music you are importing. On the contrary, for that Picard is the better tool as it allows that.
There are not many advantages of using Beets over Picard, apart from CLI, and especially for the OP use case.
Not sure if it is illegal in Germany, but laws usually aren't so specific. Where I live we basically made “From river to the sea” illegal, because “it promotes genocide”.
I recently switched to nixos which makes dependency management and configuration itself much easier. Probably the best option to run things on bare metal IMO.
Sure, I am not a fan, but I don't see any huge issue with this. Unfortunately, quite a lot of projects do stuff like this. If you are really concerned you can use matrix without using anything from matrix foundation (aside from the protocol) there are alternative clients like cinny. And even alternative servers like conduwuit.