“releasing the modified version to the public” would cover them re-closing the source and then subsequently releasing that newly closed source, so they can’t relicense it and then release the built version of the code.
At least not easily, this is where court history would likely need to be visited because the way it’s worded the interpretability of “modified” in this context would need to be examined.
Oh, yes but the DRM exemption clause means that you can backwards engineer the changes and continue releasing them under GPL
Edit: as an example we should probably be looking at the duckststion situation evolving right now:
https://vimuser.org/duckstation.html