How can I change the icon when I unlock my Macbook?

Are you referring to the Desktop (screensaver) in System Preferences?

There are a few choices to select, going into there. 'Default' ones &

some you may have added to the system; in folders can be located

almost anywhere your User name has access. Use + to add folders.

Add image folders from within the Desktop preferences panel.

The folders can be almost anywhere; somewhere easy access

for iPhone or other camera, & desktop; maybe folder in Dock.

Your 'user' icon image is another one, and I have several for

different items; so I forget which one, for email; for gmail, etc.

And one for your Apple Community account, too!

• How to change app icons on macOS | AppleInsider

https://appleinsider.com/articles/21/01/06/how-to-change-app-icons-on-macos

• Change a user's login picture on Mac - Apple Support

https://support.apple.com/guide/mac-help/change-a-users-login-picture-mtusr002/mac

• How to Change the Profile Picture of a Mac User Account

https://osxdaily.com/2014/07/14/change-mac-profile-picture-user/

• How to Change Mac OS X Icons: 14 Steps (with Pictures) ...

https://www.wikihow.com/Change-Mac-OS-X-Icons

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