When the ShowOnlyInnerProperties property specifier is used for a struct property, the properties contained within the struct are exposed to the Blueprints Details panel as if they were part of the class containing the struct property. This does not happen if the class containing the struct property is nested within another class as an instance. In this case, the struct property appears in the Details panel with its properties nested below it.
No. The same behavior occurs in 4.20.3.
In the Blueprint of the first class (step 3), the name of the UPROPERTY in that class does not show anywhere; the properties in the struct are the only properties shown. In the Blueprint of the second class (step 7), the name of the UPROPERTY in the first class is shown, with the struct's properties nested below it.
In both Blueprints, the name of the UPROPERTY in the first class is not shown.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-70288 in the post.