I want to turn off syncing to the cloud. I want all my images to live on my computer (mac pro late 2013) & how do I un-synch my synched photos. I have tried phoning adobe but they don't answer their phone (UK).
Assuming you are using
only Lightroom Classic, all your images do live on your computer. Syncing doesn't change that.
What syncing does is upload compressed versions of photos that have been added to collections which you have told LR to sync.
If you want to turn off synching, go to the identity plate in the top left of the screen where there's a little drop down. You can pause sync there. Other options are to switch syncing off for those collections, or remove photos from "All Synced Photos" in the Catalog panel. Or you can go into Preferences where there's a nuclear Delete All Synced Data button - but you're better off learning how to use or limit your use of syncing.