Hi @Picco Emiliano ,
Thanks for your detailed reply.
In order to check if there is something wrong with features of the problematic Outlook client, please try to completely uninstall and reinstall this specific problematic Outlook client and then test to see if the issue could be resolved.
By the way, I noticed that your Outlook version is 2016 version. As the document says, Support for Office 2016 for Mac ended since October 13, 2020. Feature issue might happen since lack of newer updates. If the issue still continues, for better user experience, I would suggest you to upgrade your Outlook to the new 2019 version, I tested in 2019 versions and have not met this kind of issue yet.