Maybe because the PopupField is generic, I can not find a way to create a PopupField in the uxml.
For example, can I specify a list of choices and assign integer or enum value to it in uxml? So that I can customize a different name better than the enum entry name in code.
Or maybe I have to create it from code and insert it to the proper position?
You could derive a class from the PopupField one with the type you need, and use it in uxml afterwards.
For Enums, we also have the EnumField control that you could look into.
Depending on the version you’re on, you might also have access to DropdownField, which is a simple PopupField, so you can really set any choice you’d like as literal strings.