The shortcut Ctrl+Alt+F9 is to calculate in all open workbooks, even already calculated in the manual calculation model (see how to set Calculation Option to Manual).
Please refer to the shortcut Shift+F9 to calculate only active worksheet.
Step 1: Click the cell, e.g., Cell B3;
Step 2: Change the value in the cell from 4 to 6;
Step 3: Press and hold the Ctrl and Shift keys, click the F9 key to have the calculated results.