To do Alt + M X on Mac in Excel, download and install Accelerator Keys, then press Option, followed by M, X.
Command: Calculation Options Menu
This is how to do Alt + M X on Mac in Excel with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with Excel.
Alt + M x opens the Calculation Options dropdown menu in Excel. This menu controls how and when Excel recalculates formulas, with options for Automatic, Automatic Except Data Tables, Manual, Partial calculation modes. Manual mode is useful for large workbooks where automatic recalculation would slow down your work.