I have the desktop and web Lightroom app but there is no connection between them. I have gone to identity plate set up as per instructions I found on here earlier to try and join them up and it says 'no option for lightroom or lightroom mobile identity plate'. I am signed in on my desktop.
Not sure how to get both devices to recognise each other and then sync? Please can you help?
You are using Lightroom Classic, not Lightroom desktop. Syncing the catalog has moved. Look at the Modules at the top of the main window. There is a small cloud icon at the far right. That is where you enable sync now.