macOS already does all of that for all programs. I think the main problem here is that macOS only protects certain directories and not others. Programs can request access to Documents or Downloads, or they can request full-disk access (e.g. to read Library/Messages).

For unprotected directories like Library/Keychains, programs can just copy the encrypted database. Since the malware obtains the keychain password with a fake password prompt, it can decrypt the database.