There seems to be an issue with the version of `bsdtar` that is provided by your system.
Could you please share the return of the following command, so that we may know a bit more about this tool version?
There might be an alternative that require only a slight tweak to the game script, so it does not require the use of `bsdtar`.
Open `play-baldurs-gate-1-enhanced-edition.sh` in a text editor, and look for the line 52, that should look like:
Replace this line by the following one:
Then run the script again, this time it should use `unzip` instead of `bsdtar` for extracting the game data from the installer.