Second screen turns black while requesting to join displays

[MenthaSuaveolens]

Linux mint Cinnamon 22.2

Connect beamer (Seiko Epson) via HDMI

1. Mirror displays (works ok) via control-center-app
   After presenting the desktop (how Linux Cinnamon works)
2. Trying to join the screens via control-center-app
3. After clicking Join displays, the beamer-screen turns black. The menu to confirm the change
   is on the external monitor => one can't confirm the change (on the screenshot the external screen is darkened
   (the menu isn't visible on the external screen however)
   Why isn't the confirmation-menu not displayed on the primary monitor?