To do Alt + L on Mac in Excel, download and install Accelerator Keys, then press Option, followed by L.
Command: Switch to Developer Tab
This is how to do Alt + L 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 switches to the Developer tab in Excel’s ribbon. The Developer tab provides tools for creating macros, working with Visual Basic for Applications (VBA), managing add-ins, Inserting form controls. Note: You may need to enable the Developer tab in Excel Preferences first.