For Unreal 5.3, follow @MisterPixel steps but in the EditorSettings.ini delete the lines with the CreatedProjectPaths= that point to your project folder.
Example:
bNotifyEnableS3DD=True
bEnableS3DDC=True
CreatedProjectPaths=C:\C_Unreal_Projects
CreatedProjectPaths=D:\Unreal_Projects
CreatedProjectPaths=D:\Unreal_Projects\MyTest
CreatedProjectPaths=D:\Unreal_Projects\MyFirstPersonTest
CreatedProjectPaths=D:\Unreal_Projects\UnrealEvents
CreatedProjectPaths=C:\Users\myuser\Documents\Unreal Projects
The project will disappear from the Epic Unreal Library and from the Unreal Project Browser