Excel lot of buttons greyed out

For example, pretty much all in data tab is disabled and is non-clickable

Example:

Possible solution

See the file name on top. If you see Shared, this may give a clue on whats wrong

In this case,

Check Review tab, Protect Section and see if Unshare Workbook button is enabled. If yes, click on this, and voila, all editing is back allowed!