Gravity/body weight/how the spine bend is something the apps don´t show right now, maybe there are
apps in the future which can do that. There is something you can do but that takes a lot of time,
search for a reference picture for the pose you want to draw, then model the pose with clip studio
or whatever app you are using. Then use the reference picture + the 3d model as a reference
for your drawing. The advantage of the 3d model is that you can turn it in every angel, the disadvantage
is, like you mentioned, the missing dynamic