iCloud photos
Ok so I logged out my iCloud and I signed into a different one because my cousin needed to do something and when I signed out all my photos were gone and please I need help really soon
Your primary Apple ID was say example1@icloud.com if photos were turned as on https://support.apple.com/en-in/guide/icloud/mmb1de40d9/icloud and photo library https://support.apple.com/en-in/HT204264 and its preferences were set up https://support.apple.com/en-in/guide/photos/pht5156cc968/4.0/mac/10.14
After that you sign out this apple id from iCloud.com see the article https://support.apple.com/en-in/guide/mac-help/mh36825/10.14/mac/10.14
The photos and data was saved on iCloud server , you then signed in with new Apple ID and password sat example2@gmail.com , this Apple ID will be now active in Mac system preferences and what ever data is stored will reflect in Mac by turning on iCloud features .
To access the the previous photos open a new tab ( use command and T keys ) sign in with old Apple ID and password with account credentials at www.icloud.com your previous photos will be accessed https://support.apple.com/en-in/guide/icloud/mm73262d11fe/icloud
See this article also https://support.apple.com/en-in/guide/icloud/mm8b32f3ae27/icloud