Synch not working after LR and Mac upgrade

I just upgraded my Mac to a Mac Studio, so it's now an Apple rather than Intel chip machine, and upgraded Lightroom CC to 12.4, so a new catalogue was built. All is great and spectacularly faster, except synching to Portfolio is now not working. From the Portfolio side I tried a reset on a page linked to a folder - it says that the reset has completed but hasn't picked up the changes. On the Lightroom side it confirms I am logged in and it says it's synching some photos to the Cloud but it never completes and the photos all show as "uploading". I also added a new synched folder, but it doesn't show up in the folder list if I try to add a new page from from Lightroom from Portfolio. I'm guessing it's something simple - but I'm missing it. Maybe I just clear everything from my Cloud store and start synching again. Any ideas please?