actually, the Enable Notification logging feature is intended to suppress any notification. It’s just caught in the log for the reference.
It’s a bit confusing. I install a plugin, test and nothing happens… ?!
Now, what’s the case exactly with Gutenberg? Which Trigger are you using and what’s the expected result? How do you test?
The problem can be reconstructed. I just tested the plugin again on another website. Here the same. If “Disable Gutenberg” is active, no mail notification for post changes (post published / addet / updatet) will be sent. When “Disable Gutenberg” is inactive, your Plugin works.