In 14.5, per
CMS-12620, Visual Editing supports adding and removing fields in compounds.
However, it does not take into account the maxitems setting, as documented at https://documentation.bloomreach.com/14/library/concepts/editor-interface/limit-the-number-of-fields-that-can-be-added-to-a-multiple.html
This goes for multiple properties (already there before 14.5), multiple compounds as well as for content blocks.
A) If a user tries to add an extra field, either in content blocks or multiple compound, there's a toast message "Failed to add a field value" and a back-end logging:
In the content editor, the presence of add/remove controls react on the maxitems settings, plus there are hints.
B) For a required multiple compound field, a user cannot remove an already added value, then add a new one. So for Content Blocks, this prohibits replacing one type with another.
Maxitems for multiple fields:
Maxitems for multiple compounds: