Previously, I haven’t reply on my computer, so I could’nt elaborate!
Skeletal mesh and skeleton consume ressources,
It’s better to make a material with WPO to mimic wind or to use the clothes tools in unreal.
You don’t need bones and to use the clothes tools in 3dsmax.
All you need is a very simple model (made in 3dsmax), no bones, no clothes modifier in 3dsmax
Use the unreal tools.
As you noted “it is just the mesh- there is no skeleton or bones in it” => this is the point!
You can download the “content example” in the epic launcher and if I remember, there is a flag so you can learn from it to make one yourself!