Photos in iCloud

Yes, iCloud Photos does not store or back up photos that have been removed from other connected devices. All changes are reflected on all devices that are connected to this iCloud account.

The feature "iCloud Drive" within iCloud would be a way to store data in iCloud.

Set up iCloud Drive - Apple Support

Can you see the missing photos if you log into your iCloud account on your computer and open the Photo App?

Did you already check this article?

If you're missing photos or videos in the Photos app - Apple Support

As a start, check this article:

Get help with iCloud Photos - Apple Support

In general, adding or deleting photos and other changes on your device will also add, remove or change the content in iCloud and on all devices that are connected to this iCloud account.

Sorry, but if the photos are not part of the "Recently Deleted" folder, or some other album, the photos got somehow deleted or damaged in another way. And it's hard to find a reason for that after such a long period of time.

Any chance you also created backup on your computer after you returned from your holidays?

This backup might contain those missing photos, but you'll have to restore from the whole backup, since parts of the data can't be extracted.

Before you start, make sure to have at least your current photos saved to an external HD, just to be sure.

Here's how to do that:

Archive or make copies of the information you store in iCloud - Apple Support

If by any chance your missing photos have been moved to the Recently Deleted folder on your device, they would have been deleted automatically after 29 days, which you might not have noticed. And deleted photos from that folder can't be restored at all, sorry.

Are the missing photos still on your iPhone or another connected device?

If they are still part of your photo app on your phone, connect to Wi-Fi and try to upload them again.