You have created a folder on the desktop ( right click on desktop and created a new folder ) , and then exported photos in it and also many photos are directly exported on the desktop , as per this article https://support.apple.com/en-in/guide/photos/pht6e157c5f/mac
You have to set up iCloud photo library see this article https://support.apple.com/en-in/HT204264
And its preferences https://support.apple.com/en-in/guide/photos/pht5156cc968/4.0/mac/10.14
Then open finder > click on desktops > again tap the folder that was created on the desktop , and select all of them ( use command and A keys ) , right click on them and share with photos , apple the same method for many photos that are saved separately on the desktop .
All the folder photos / separate photos will get transferred in system photo library folder of the photo application see this article https://support.apple.com/en-in/HT204414
Note : it seems that few Macs ( 5 in number ) are signed in with same Apple ID and password on the same network , and all the folders with photos / separate photos will be mirrored on the desktop .
You can set up iCloud photo library for all of them so that no photos will ever mirror on the desktop of each Mac , and only will be saved on iCloud server .
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This is photo library folder .
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