Magic keyboard won't pair

My magic keyboard (a misnomer if ever there was one) stopped working some months ago and I have been using a wired keyboard but now i need to use the one that was matched to my old iMac running Monterey. But it refuses to pair. I have tried brand new batteries, various keyboard presses and turning BT on and off. I sometimes get the code to enter, but Monterey won't wait, or if I do manage to send the code back, the keyboard doesn't connect. I have also tried deleting the plist file and rebooting countless times. The keyboard sits about 3cm from the iMac, and the only other peripheral using BT is a magic mouse which does magically work as it should. There is no interference, no lead barriers or other obstructions. I think someone is going to shout SEQUOIA, and I will try that or Sonoma if there is any suggestion adding more operating systems will help this issue. Are there any other ideas that have worked for this rather vexing issue. THank you.