That game update has been released (as well as a hotfix for a couple of new issues that that introduced). The current game version on PC is 3.6.58.1306.
If you updated to Catalina again, it made changes to
how file permissions are handled. Usually that blocks the game from even seeing the profile(s), but it wouldn't hurt to check, in case restoring from the backup half bypassed that.
In System Preferences, Security and Privacy, Privacy, click on 'Files and Folders' to get a list of apps that have requested folder access, and allow D:OS 2 access to the Documents folder, if applicable.
Try verifying local files:
Terminal
cd ~/Library/Application\ Support\ ... up to the Divinity Original Sin 2.app folder
codesign -vvv Divinity\ -\ Original\ Sin\ 2.app
For the first command, it may be easier to browse to the install folder in Finder, then drag and drop the location into an open Terminal window.
The second command takes a while, and will output some lines starting with '--prepared' or '--validated'. If everything is fine, it will end with:
Divinity - Original Sin 2.app: valid on disk
Divinity - Original Sin 2.app: satisfies its Designated Requirement
If you create a new OSX user account, start the game from there, create a profile and start a new game, are you still getting the same error when trying to save?