Hi Joe,
Thank you for posting in Microsoft Community. I'm here to help!
This usually happens when the range you’re copying doesn’t match the size of the range you’re pasting into.
To fix this, make sure the destination cells match the shape of the copied data. For example, if you copy a 3x3 block, select a 3x3 block before pasting. If you want to paste into a different size, try Paste Special > Values or Transpose to adjust the layout.
You may refer to this article for more information: https://support.microsoft.com/en-us/office/i-can-t-copy-and-paste-data-on-my-sheet-in-excel-for-mac-f046b142-dfc1-4d33-a730-f94c45c2da13
I hope you find this information helpful. Please let me know if you have any further questions If the answer is helpful, please click "Accept Answer".
Regards,
Carlo