Cheers, opening System Settings and then Option clicking Displays, did the trick and showed the rotation option for the built in display. It's mostly PDFs I'd be reading so might try the PDF reader option, as yeah, navigation using the trackpad after the screen rotates is challenging.
Edit: Just tried rotation in the built in MacOS Preview app, (Command+R or Command+L) and works really well. You do have to set the View to Single Page, and rotate each page separately (it does remember which pages were rotated), but other than that it's great.
https://discussions.apple.com/thread/255072447?sortBy=rank
FWIW, it's easier to rotate the view in something like Acrobat, and then you don't have issues w/ the cursor direction.