My Magic Mouse is not working

Yesterday, when I turned on my iMac, I received a small screen that I need to connect a wireless mouse, I did that with my Magic Mouse but nothing ever happened.

I tried watching videos on how to fix it and reconnect it, but I couldn’t get it reconnecting. I had to forget the mouse from my Bluetooth and I can’t get it to recognize the mouse anymore.

I tried turning the Bluetooth on and off, restarting the iMac, but I could not get it reconnecting again.