I have fixed it now. All the binaries had lost the executable bit, which you can remedy with chmod u+x foo, and all the symbolic links in the framework had been destroyed, which you can recreate with ln -s foo bar. I also tried unzipping the original archive in several ways, with macOS Archive Utility, MacPaw's The Unarchiver, Keka, with unzip in Terminal etc., and it always unzipped fine, but still resulted in the above broken app bundle. It seems that the initial error was made when zipping the app, which I assume was not done with the proper tools or settings.