Suddenly one day the calc sheets (any I open) began looking like they are sitting on paper with dots all over it. (Like LiveScribe paper if you know LiveScribe.) Tiny light dots all over - no real pattern, just an odd background. I have put up with it for several months. I must have hit some keystroke by mistake. Have you seen this before? Is there a fix?
You have set the Grid to show.
In Tools > Options > LibreOffice Calc > Grid set “Visible grid” to unchecked.