So, I'm guessing there's no US-style (and more rencelty, also Russian-style) registration requirement and self-disclosure for such financing, for people involved in politics or influencing operations? Any proposals/discussions to have something like that enacted? Or is something like that a non-starter in Germany?
Since Jan. 1st 2022 Germany has a "Lobby Register", where people and organisations have to register if they want to influence members of parliament or government officials on their own behalf or in a role as professional consultant to a third party. This applies to domestic persons and organizations as well as persons and organizations from other states (there are a few exceptions, e.g. for humanitarian organizations without a permanent address in Germany, details see the "Lobbyregistergesetz" (German)).
As far as I can tell, this is a lot less draconian regime than the US and Russian laws (failing to register carries a maximum fine of 20 000 Euro rather than getting the organization in question banned or anything like it), but it is the closest thing I could find.