I can't see my iphone in itunes or finder on my mac.

I have just updated my phone to v14.1 and my mac is High Sierra 10.13. My phone is definitely being read by my mac as I can upload my photos and it is visible under usb in finder. However, it does not let me run a backup of my iphone or access my music to change playlists etc.

I know I have an old machine but it works perfectly fine for what I use it for, except for this issue which has only come about with the new software updates. I really don't want to (can't afford to) buy another mac.