i select a vert and press I but nothing happens
Use AnimAll addon from the addons inside Blender.
edit: you can’t directly animate a curve vertex, except with Animall or with shapekeys as Alexander_Sokerov or Upliner say, but it’s limited, the other solution is to hook the vertices to empties or bones, tell me if you need details
You can just use shape keys
oops yes you’re right, it’s also limited though