So I've got cyberpunk phantom liberty 2.0 but to update to 2.1 heroic game launcher wants me to download the hole game again, gog galaxy through wine is not an option so I'm looking at xdelta3 and innoextract to manually patch game files. But I'm hitting a break wall and seems to fail with every attempt using xdelta3
I have no idea what problems you are hitting or seeing, so I think that it'd be hard to offer much advice outside of long-shot guesses.
I've used xdelta, albeit not for GOG games, and didn't know that they used xdelta for updates. I mean, it works, given a valid patch file and the right source file.
Are you sure that the source file is the correct version? What output are you seeing when trying to run xdelta?