Ipad / iPhone not sync'ing photos from the Photos app

I have an iPhone 12 Pro Max, iPad Air, 3rd generation, MacBook Pro 16", 2019. The software is up to date on all of them.

All my photos (12,000+ of them) are held in Photos on my MBP, in separate folders (see image below).

When I try to sync my iPad or iPhone the photos sync part gets stuck in what seems like a continuous loop (see images below) and refuses to sync any. I can choose to 'Skip Photos' and the app then syncs other documents before finishing normally.

I don't use iCloud for sync'ing due to the volume of images that I haVE.

This seems like a bug - how can I sync my photos to my iOS devices?

Hugh