Thank you to all who replied: I'll have a go with your suggestions and let you know how I get on. I think you might have a point about Mojave, Lobo: it seems to have broken more than just how the mouse behaves... my WiFi drivers appear to have issues as well.

Thanks again!

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks