I assume that you don't want to disable right-click functionality entirely, just the formatting box (font name, font size, etc).
There are two ways to do this.
The first, and easiest, uses the Visual Basic Editor (VBE) Immediate Window.1. In Excel, press Alt-F11 to open the VBE.
2. Press Ctrl-G to open the Immediate Window (or open it using the View menu).
3. In the immediate window, enter this:
Application.ShowMenuFloaties = Application.ShowMenuFloaties
(Yes, it looks strange as there's no 'Not' or 'False' but it's correct.)
4. Press Enter.
5. That's it - the little toolbar is now gone.
6. If you want to re-enable it, do exactly the same again - the command is a toggle.
The second method involves editing the registry. You should only do this if you are confident with the registry - and always make a back-up first in case something goes wrong.a. Open Regedit and navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Toolbars\Excel
(for 2013 the version number is 15.0 instead of 16.0; 2010 is 14.0, 2007 is 12.0, 2003 is 11.0)
b. Right click on the RHS and choose New then DWORD (32-bit) Value
c. In the value field enter AllowMenuFloaties
d. That's it. Don't alter any values. Just close regedit.
Edit: I see I was beaten to it with the registry edit info, but I'll leave it here anyway.
Edit 2: If you try the VBE solution first and then go to the registry, you'll find that the DWord is already there. A value of 0 is 'don't display' and 1 is 'display'. If you've amended the 'Mini toolbar' option in Options (as you said you tried) there will also be a DWord for it: 'AllowSelectionFloaties' - also 0 = off, 1 = on.
Hope that helps.
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