Good day lorenzo_b
Merged cells restrict what you can do to cells/columns and rows, you should consider using “Center Across Selection” instead. Please follow these steps to achive the same result but without the restrictions of merged cells.
1 - Select the cells that you want to “merge”,
2 – Open the Format Cells dialog box (Home Ribbon, Font group, little button in bottom right or right click and select Format Cells from the list) or better still Ctrl key plus the number one key, Ctrl+1
3 – On the Format Cells dialog box, go to the Alignment tab and on the “Text alignment”-Horizontal, select the “Center Across Selection” option and click OK.
Your work sheet will look like one with merged cells.You can get the same look on your worksheets using either merged cells and Center Across Selection methods but if you need to use your data to do further operations, like sorting, or inserting rows and columns using merged cells, you will be restricted. With Center Across Selection you will not have this kind of problems.