Connecting iPhone Xs max to iTunes

I have a new iphone XS max. I installed data etc from my previous iphone via an icloud backup. I now want to sync my new iPhone to iTunes and copy my music library onto the new phone, as well as copy photos on my phone to my photo library on the iMac. However when I connect the phone to the iMac via a usb cable, iTunes doesn't recognise the phone. The phone makes a beeping sound, and a notification saying 'Trust/Don't Trust this computer' flashes (too quickly for me to say trust).

I've restarted iTunes, the iMac and the iPhon, and also tried different usb ports. Same problem.

Help please