There are multiple select menu attribute types. Below is an explanation of each type.
The Select Menu attribute allows you to build a select menu with your own options within it. You can specify text to show before and/or after the field.
Values for the select menu attribute are set up in the Values tab when creating the attribute.
Select Menu - Countries
Select Menu - Countries displays a select menu of countries. The countries can be configured under Site Settings.
Select Menu - Display attributes when selected
Select Menu - Display attributes when selected is a select menu that can be used to show other attributes on the admin form based on the value selected.
In the Values tab, you can give each option a name, set whether it is the default, and choose which of your content layout attributes show when the option is selected.
Select Menu - States
Select Menu - State displays a select menu of US states.
Select Menu - Yes/No
Select Menu - Yes/No displays a select menu with two values: "Yes" and "No". The value saved will be 0 for No and 1 for Yes. You can treat that as a boolean value when used in your content templates.
Select Menu using data from an App API call
The Select Menu using data from an App API call is an attribute that pulls in data from other apps into the select menu. For example, a Blog Category Filter API could be called to list all categories for the Blog app into the menu.