Fritz has always been a combination of a GUI and an engine. I think at first it was just a cut-down version of ChessBase, rather like ChessBase Lite but with an emphasis on playing. At some point they changed the GUI so one could add any UCI engine. FatFritz is NNUE enabled, and the first version is GUI + lc0 + net. FatFritz2 does not use the gpu but uses only the cpu, and is GUI + stockfish + net. So the answer to your question is:

ThinFritz

• GUI = ChessBase
• engine = licensed from third party author

FatFritz

• GUI = ChessBase
• engine = copied (legally) from lc0 (v1) or stockfish (v2)
• net = by Albert Silver, either owned or licensed by ChessBase, that's between them

Well the compensation is that, when they copy Komodo Dragon for Fat Fritz 3, Kaufman will sue because it is copyrighted.

https://github.com/DanielUranga/Stockfish/commits/ff2

The networks are completely different, and they have released the source and (soon, i think) the actual network on github. There's no violation of GPL and no ethical problem, in my view.

Thanks for the link. My German comprehension is not great if the subject is not chess moves, but the Apple translation worked fine for me.

My reaction when I saw the product announcements on en.chessbase.com was they are actually selling the customized neural net by Albert Silver. Therefore I didn't think it was _so_ bad. But this article throws a different light on it. I think the mispelling Stocksh shows an ill intent of ChessBase towards their customers. And looking at the (I think second) article again
https://en.chessbase.com/post/fat-fritz-2-best-of-both-worlds
it now seems to me that it's couched in a way to minimize the dependence on Stockfish 12. But I missed that at first reading because I'm familiar with the story, so I sort of filled in some of the blanks myself as I was reading.

Of course there is a long tradition of slick commercial chess programs having somebody else's engine under the hood. But those would have been commercial arrangements, and the consumer was not only paying for the strength of the engine, but also the useful packaging. I have in mind the Chessmaster series, and another example for me was something called Sierra Chess Complete. No doubt there were other cases.

This is different, because they didn't pay the engine author(s), and more importantly they are directly marketing the strength of the engine itself, even saying it is stronger than Stockfish 12. For a long time I didn't realize the ChessBase part of Fritz is just the GUI, and the engine has always been by someone else. When Rybka became Fritz is when I finally figured it out. I guess from ChessBase's point of view there's really not that much difference between a commercial arrangement where they are obligated by the author to pay, and a similar commercial (sic) arrangement where they are not obligated to pay and therefore they don't. But from an outside viewpoint I think it's a good illustration of Sorite's paradox, aka the fallacy of the beard, which I like to restate as "a difference of degree becomes a difference in kind".