Good evening Dario and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the issue you have encountered with the Add new organizer button.
I would love to help you with this topic.
As a first troubleshooting step, could you please provide us with your system information in a private reply ? (following the instructions found in the link)
Furthermore, if there is a dummy login (non admin account) I could use to test the functionality on your website, that would be great (since I am currently blocked from seeing the actual page).
Finally, if you are able to, could you send screenshots of your settings for the tab found under Events -> Settings -> Community ?
Best regards,
Geoff B.