How can i unlink some object that I linked without want?

Hello there,

On my adaptation trip for the anytype use, i’m having some difficult to understand the most value tool of this app: the links and graph view.
Even though the program occasionally behaved strangely (see other posts I made and highlighted unknown properties), I have tried to use it. And unlike other times when my problem was linking one object to another, I can’t now undo the link (since the property is restricted). How to unlink an object?

Is it a custom Relation?

Can you please provide a screen-shot?