To do Alt + L C on Mac in Excel, download and install Accelerator Keys, then press Option, followed by L, C.
Command: Combo Box (Form Control)
This is how to do Alt + L C 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 + L c inserts a Combo Box form control. A combo box displays a dropdown list of options that users can select from. You can link it to a cell range for the list items and another cell to store the selected value.