Excel in OneDrive and on Mac.

Hi everyone,
I am working in Excel on a Mac and I cannot add a logo in the header, or type in the footer. all of the ribbon is greyed out so I can't select insert date. I have checked on Microsoft 365 updates are automatic. I have put the spreadsheet in page layout view. I have checked the margins. I have downloaded both documents one contains the logo picture, and the spreadsheet, but still unable to click on the image to paste it in the header. I have checked help function, and worked on it for several hours, but still unable to use it.
Cheryl.