Suddenly experiencing a problem with Excel 365 UI where certain areas of the screen (typically menus with box surrounds) where markings appear. See picture. This only happens after a number of hours running excel during the day.
Excel 365 can be tricky with UI issues, especially when the ribbon or menu layout doesn't display correctly. It might be due to a corrupted add-in or setting.
Try starting Excel in Safe Mode by holding down the "Ctrl" key when launching the app. This will disable add-ins and may help identify if one of them is causing the problem. If Excel works fine in Safe Mode, you can disable add-ins one by one to pinpoint the issue.
For more tools and tips, you might want to check out some resources for excel online. It often has unique solutions and updates that can be beneficial. Also, clearing the cache and repairing Office from the Control Panel can fix glitches.