The notebooks were transcribed to regular German by a couple[0] who learned Gabelsberger just for that purpose. There is a bunch of analysis of them in Gödel's 5-volume Collected Works, iirc mostly volume 4. I'm surprised if there was any interesting mathematical content left to be found. The question that mathematicians wondered about the most was whether Gödel made any progress on the independence of the continuum hypothesis and axiom of choice (both later proved by Cohen). It appeared that he had some thoughts about it but didn't get anywhere. The Guardian article says Gödel was close to a proof of AC's independence but I'm skeptical.

The question the public wondered about the most was the loophole Gödel claimed to have found in the US Constitution, but they didn't find anything about that.[1]

There's a cool suspense novel "The God Proof" about finding a lost Gödel notebook extending Gödel's ontological "proof" of the existence of God.[2]

0. John Dawson (a logician) and his wife whose name I think is Cheryl (not sure). John Dawson later wrote the Gödel biography "Logical Dilemmas".

1. https://en.wikipedia.org/wiki/G%C3%B6del%27s_loophole

2. https://jeffreykegler.github.io/personal/gp/God_Proof.pdf

Trump has been showing the loophole in real time. He would have shown more if the Democrats hadn't won.