It may be part of the same problem. Please email supportdos2@larian.com with a save or two (or a Dropbox or Google drive link, etc), and I can check it/them here. If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder.
For the App Store version, each save is a folder in the /Users/<UserName>/Library/Containers/com.larian.dos2/Data/Documents/Larian Studios/Divinity Original Sin 2 Definitive Edition/PlayerProfiles/<ProfileName>/Savegames/Story' folder.
In Finder you can zip a file or folder by right clicking on it/them and selecting compress.
With the error starting after an OS update, that was likely the issue, but if restoring a backup didn't help, there may be a problem with the saves themselves.
