In the old excel, I put a "toggle read only" button on the task bar.
Clicking it made the current spreadsheet read only; clicking again made it
read-write again.

The new excel has the same icon, but it won't toggle. Clicking it makes the
current spreadsheet read only; but clicking again, I get a message that the
current file is locked for editing by another user.

How can I get it to work the way it used to????