My iMac will not open System with all icons present. I'm using OS Catalina (10.15.7 )

I did something in System Preferences yesterday and as a result, it will show System preferences but without all the icons. All I get is a narrow strip with my ID in the left hand corner and opposite, 2 icons showing Apple ID and Family sharing.

When I click on the Customise it shows all of the icons, but with a little square attached, like this.

Iwouldalso like remove the little white squares as well as restore SP to its original appearance.