Enum selection field in component

You can’t define something like that using a content-browser created enum from within c++. You need to create the enum in c++ or use a blueprint-based property.

For reference, this is how you do it in c++:

UENUM( BlueprintType )
enum class EUserDefinedENum : uint8
{
  U_SomeValue,
  U_SomeOtherValue
};

UPROPERTY( EditAnywhere, BlueprintReadOnly, Category = Classes )
EUserDefinedEnum MyEnum;