The button to affect a tag to a content is only available in the plugin web but it should be available in the plugin CMS.

That's very strange because the tool to define the tags is in the plugin CMS, but we can't do anything with these tags unless if you have a metadata defined with the tag widget.

You can search for the following sentence in cms-ribbon-content.xml in the plugin CMS :

<!-- <control id="org.ametys.cms.userinterface.Tag"/> FIXME affect tag action missing for CMS? only in WEB -->