I know the feature is still being released but I haven't found any report of this so I'm leaving it here in case it becomes useful.
The new modern tagging interface in lists a) doesn't visually differentiate the terms that are available for tagging and b) it allows you to use terms that are not available for tagging. The autocomplete experience on the other hand, works as expect only allowing the correct terms.
Here are a few screenshots to exemplify:
Term configured to prevent tagging
Autocomplete correctly doesn't display the term
Taxonomy picker doesn't visually differentiate if terms are available for tagging and worst, allows incorrect selection