Lightroom not syncing and freezes

Over the last several weeks, LR classic does not synch.

When I click on sync, it starts off by showing there are over 22000 files to sync - it then just hangs and then the number increases. It then slowly decreases, and when I leave it overnight, it has come down by a few numbers.

When I view LR again, it just freezes and I have to force quit. Sometimes I get a message that says not enough application memory.

I am running an iMac with 16 GB RAM and a 512 SSD hard drive.

My actual images are in external drive and the catalog is in my desktop hard drive.

I am now unable to sync my files and my collections - I can sometimes run LR by pausing sync. But then I am unable to sync my collections - when I do that, it starts off with the 22000 or so files syncing message.