Importing images takes 3-4 minutes per thumbnail

Since updating to LR Clasic V12.2 my editing workflow has become unuseable. When importing images it takes around 3 or 4 minutes for each individual thumbnail to show up in the library module if it shows up at all. As you can imaging, this makes working to any deadline almost impossibe. I have tried going back to a previous versionof LR  but the problem now seems to be embedded. As a final resort I have uninstalled and then reinstalled V12.2 and created a new catalog and the problem still persists. All of the images in my library have been saved with xmp sidecar files but when I try to re-import a folder, say for example December 2022 which contains 35 images, it tooks over one hour to import and even then most of the thumbnail squares were greyed out. I really need to sort this out soon because the alternative would have to be cancelling my Adobe subscription and moving to another third party editing app.

My system is as follows:

macOS Big Sur

Version 11.7.1

iMac (Retina 5K, 27inch, Late 2014)

Processor 4Gh Quad-Core Intel Core i7

Memory 32Gb 1600 MHz DDR3

Startup Disk SSD

Graphics AMD Radeon R9 M295X 4GB

My Lightroom Cache is set to 50Gb

Graphics processor trurned off (It makes no difference when turning this on)

BH