I have written several times in the forum that a simple animated vertex shader/material would solve a lot of things without having to import ready made animated plants.
Heres one link for some info and inspiration: https://blogs.unity3d.com/2018…erials-with-shader-graph/
As you can see it can be used for grass, tree leaves, flags and even animated fish.
And here is another one:
The most simple one would only need controls for sine speed, sine frequency and sine amplitude.
It's not as advanced as imported animated trees but to have some motion in leaves and grass would add life and it's as far as i understand quite easy to implement.
For more advanced animated plants I use Plantfactory or Speedtree. FBX is a much used format for animated content.