bluetooth mouse & keyboards won't connect

I've always had issues with the bluetooth connecting with the mouse and keyboard.. it's always been flakey but now it's died entirely.

I recently installed Wacom for a tablet and I know there can be issues when installing a new app; but I can't just uninstall it! I need to use the tablet!

I have tried everything: unpairing. bluetooth off/on. wifi off (using ethernet).

Exasperated, Sussex.

iMac 2007, Big Sur 11.4. (can't upgrade to Maverick until I clear off photos but that's another issue!)