Universal Control does not work. It says, my MacMini M1 2020 is not supported.

Good morning,

I just installed iPadOS 15.4 and MacOS 12.3 and wanted to try out Universal Control. First I must say that there has been an issue while updating my iPad 9th Generation to iPadOs 15.4. After download was completed there was a Pop-Up asking to enter a code as I clicked on "Install now". My code was deactivated before on the iPad. A relative had exactly the same issue and I found out through web search that this issue had been there before, concerning especially iPad Pros. My relative also had this problem before. We live in Germany, so this time it might be a problem concerning the German version (if this exists). Anyway, I found out that I had to reactivate a code and then it finally worked.

Now I wanted to try out Universal Control.

On my Mac Mini M1:

Bluetooth is on, I checked the boxes under System preferences > Display > Universal Control. I can't check the third field "Reconnect automatically with Macs or iPads nearby", it simply won't let me do that. There is no field where I could add another display (the iPad). There is nothing like a "+"-Button. This was recommended by an online instruction of universal Control. My display is an Apple Cinema Display 2007 connected via HDMI.

On my iPad 9th Generation:

Under "General" > "Airplay & Handoff" is activated, also "Cursor and Keyboard (Beta)".

Bluetooth is active on booth devices. I managed to connect both devices to the point that a number was shown (from the iPad) on my MacMini which I had to confirm with a click. The devices are shown on my MacMini and my iPad, but when I want to click connect, it says my Mac Mini M1 is not supported. I had several Bluetooth issues with my MacMini M1, as have many others, and I'm wondering if there's the problem. Many thanks for any help!

I just found an advice that there must something be activated through iCloud, but I can't find anything about it. I'm not using 2 factor authentification.