Just adding a +1 on this issue as I've just discovered it with a slightly different platform combination
MacOS 12.7.4 (I know ;-)
Safari 17.4.1
Enpass 6.9.5 (1640) Mac App Store
A couple of observations in case they help you debug:
The tinymce instance will sometimes initialise, but then the content within it's embeded iframe appears to be wiped after being initialised.
If there are multiple TinyMCE instances on a single page one will load, but subsequent ones will not initialise.
To me this would point to Enpass trying to detect the content type of the field and blocking for some reason. But that's just a wild guess!
