Open Radar

 
Have an executable script. e.g. `ls.sh`
#!/bin/sh
ls

Verify that is is executable in bash.
> ls.sh

Open it with TextEdcit
Insert a newline
Save

Try to run it in Terminal again:
> ls.sh
zsh: operation not permitted: ./ls.sh

Note that TextEdit has slammed a quarantine attribute on it
> xattr -l ls.sh
com.apple.TextEncoding: utf-8;134217984
com.apple.lastuseddate#PS: ??a
com.apple.metadata:_kMDItemUserTags: bplist00?
com.apple.quarantine: 0086;619612f1;TextEdit;

Although TextEdit does have the 
com.apple.security.files.user-selected.executable

entitlement, allowing exectuables to be openend and edited.

Side Note: 
If you dont' use the NSDocument based safe write routines, but just open that file directly and replace its contents evertyhing is fine. Which is a shame, so this isn't a security feature to not alow editing of scripts, it is just a bug when using the NSDocument based writing routines adding quarantine on overwrite too.

This was a problem for SubEthaEdit as it was using NSDocument based methods, now it uses the less "safe" just overwrite in place methods to work around this. which is unfortunate.

This behavior appeared in Monterey 12.0.1 for us. Big Sur does not have this.