Thousands of photos missing from Photos... (Not the Album issue)

Thousands of my photos have disappeared from the photos app. I have 2TB iCloud and everything had been working fine (syncing across iPhone, iPad, MacBook and PC). I'm talking now about the normal camera roll and not albums.

I went to show some colleagues photos from a family holiday in 2018 and there was only 1 photo. I searched using maps and also on the date and there is nothing there. Nothing (other than the one photo). I checked on the Mac, the iPad and the iPhone and obviously these were all the same as they are all connected to the same iCloud account. I have Checked iCloud Photos on the web, and they aren't there.

However, I have a PC that I use for gaming mostly, and it has the iCloud app installed, and guess what. All of the missing photos are in the iCloud photo directory on the PC.

I then thought there was some weird sync issue and that they were locally on the PC, but they aren't. They are in iCloud, but only visible in the iCloudPhotos app on the PC. This has happened since the upgrade to iOS 18.

I'm currently downloading them all to a backup folder on the PC. I really can't have years of memories disappear like this. It's incredibly frighting. The irony is that they are still in iCloud storage somewhere, but that the only way to see them is the photos app in the PC.

Has anyone had a similar issue? Is there any way to browse the photos files in iCloud? Any advice would be really appreciated, but its looking like I'll need to go back to using OneDrive - but I'd really rather not.