I recently reinstalled The Witcher: Enhanced Edition on my Mac via GoG Galaxy, using the new Mac OS-native version of the game. None of the additional adventures (Side Effects, Price of Neutrality) are available for play. I seem to recall them being playable in the past when I was previously using the older Wine-based version of The Witcher for Mac. Am I missing something here? Is there anything I need to do to enable them?

I don't think the devoloper who ported the game also ported those extra adventures. Kinda lame unfortunately.

If you can get your hands on a Windows PC with the game installed (or a copy running under Wine), you can find the adventure files under
\Users\Public\Documents\The Witcher\

Copy those files to your Mac under
~/Library/com.cdprojektred.TheWitcher/The Witcher/

I have uploaded a 7-Zip archive for your convenience, because I’m not sure where to find one.

Thank you so much for the files! I've got exactly the same problem and tried solving it your way but I couldn't find the MAC folder 'com.cdprojektred.TheWitcher', it is not there. There's a 'Witcher Enhanced edition' folder in my applications but then I don't know where to put the .adv files? There are 'contents' and 'resources' folders in it and there's a lot of different folders inside them as well. Does anyone know where should I put the .adv files so that they work? I tried putting it in a few places but it doesn't work :<

You should copy the files to `~/Library/Application Support/com.cdprojektred.TheWitcher/GameDocuments/The Witcher`. The previous paths mentioned here lacked the "GameDocuments" part.