There's a feature in Excel for Mac that many people have been asking for. The "Customize Keyboard" feature is now available. To get the update, go to Help > Check for Updates, and update to version 16.18 or greater.
You can now assign your own key combinations to many commands within Excel. Just go to the Tools menu and choose Customize Keyboard. Pick the category of command you’re trying to find, and then search or browse for the command in the list. Select a command, press a key combination, and see if it’s used already. If it’s already in use, you may want to pick a different combination. Then just click the “Add” button to assign the key combination to the selected command. Read more details here - Create a Custom Keyboard Shortcut. 
We'd love to hear your feedback about this feature and of course we want to know if you run into any problems, so please click the Smiley-face button in the top corner of the Excel window to send us feedback.