Don’t know the situation in Germany. In Britain found treasure is ‘treasure trove’ and property of the Crown. But the Brits are smart in that regard. They pay fair market value for whatever the Crown (usually museums, etc.) want to keep. The finder gets paid and whatever coins or treasure aren’t interested in. That way, people aren’t encouraged to keep such finds to themselves and the finds are able to be studied scientifically by experts.
A quick search indicates that in three “states” in Germany that if you find stuff on non-historical sites (like farmland with no known old battles, etc.) it is split 50/50 with the property owner unless another arrangement has been made.
In the rest of Germany, the government gets to keep all of whatever they deem is of “archaeological importance”, with the detectorist or landowner getting nothing.
Although I suppose the landowner does get a pre-dug swimming pool for the months that his field was out of production.