Here a Samsung moderator, now retired, (unfortunately this forum has become also without a skilled moderator about WFS and Android) answered vaguely like I wrote in my previous post:
If you search through this forum you can find many post here and there about it.
As I mentioned in another post, also official Samsung watchfaces are made with Android Studio. So for now there is not another way. Let’s see what will be with the next version of WFS.