To do Alt + L B on Mac in Excel, download and install Accelerator Keys, then press Option, followed by L, B.
Command: Button (Form Control)
This is how to do Alt + L B 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 b inserts a Button form control. After selecting this tool, draw a button on your worksheet. You can then assign a macro to the button, allowing users to run the macro by clicking it.