Also, dragging the canvas with the hand tool at 50% or higher magnification has also started lagging. This just started happening today and I don't know why. Checked windows update and there were no updates applied since last month, and I haven't installed any new software or changed anything. I did notice my C drive lost about 10 gb of space and is down to 39gb, but I don't think that should have anything to do with it as I changed the krita swapfile to operate on the D drive. Any clues as to why this has suddenly started happening and what I can try to fix it? It's really made drawing frustrating, to the point it's almost unusable for me.

Check whether reinstalling the display driver makes a difference; check whether canvas acceleration is still enabled; check whether switching between opengl and angle makes a difference; check whether there's some other process running that takes a lot of CPU.

Thank you! Upon further investigation I discovered that the lagging only happened when I was using my tablet/pen shortcuts to activate panning and rotating. Using the mouse shortcuts or selecting the pan tool worked fine. It still had me stumped though because nothing in the OS or the tablet drivers had been updated (I checked). I went into the settings and saw that canvas acceleration was turned off. I don't know if it was always like that or somehow got switched off, but I turned it on, using openGL and panning and rotating is working smooth as silk with my tablet again. Thanks, you saved me a lot of stress and frustration!