HI Jesse Pena,
It is not possible to show a Enumeration value in a textbox, if you wanted to show , then you have create a new String attribute and populate the attribute based on the selected Enum value ( How ever this is the good practice i do) .
For your Second question :-is there a way to only display first four characters of an enumeration caption?
Yes you can make use of combination of Substring() and getCaption() in the Screen shot you have attached.
Ex : Substring(getCaption(EnumAttrtibute),0,3) .
Hope it helps
You can use getCaption() and getKey() on enumerators to get their relevant values. More info here:
https://docs.mendix.com/refguide/enumerations-in-expressions/