This method ^^^. This is also best because you may only want the number to show in the kitchen but not on the customer’s receipt (as it can be confusing to read when showing item number and quantity).
Just like @QMcKay mentioned in the other post about your Chinese Name product tag.
Also, if you want to display the item number on the button, there is a quick way I developed for a client before using a SQL script to automatically add the item number, you can see how to do it here: