The cursor is just fine on laptop - but on a 4K screen it is very small (looks like a single pixel).
Simple suggestion - have an option to change the size of the cursor.
You haven't said which OS but I'm guessing Windows? It sounds like a scaling issue and you should be able be able to change this, and overall applications' DPI in Windows system settings > Display. You could also look at accessibility settings. Plus I believe if you right click on the app launch icon there should be tweaks you can make for scaling Joplin.
Thanks for the reply - yes, I really should have given details about my OS. Not Windows but Linux (no bloat, no spyware 
). I probably could have worked out a fix, but I have only recently migrated to Linux. BTW, other than this very little niggle, everything else works perfectly on Linux (including cursor size on a regular screen) - so not a big issue, but I thought it would be worth letting you know. If I figure out a fix, I will post it here.