Clouds are visual manifestations of underlying weather phenomena, and only appear when the relative humidity exceeds 100%, and condensation occurs.
There are a subset of phenomena such as strong thermals and CAT which may not involve clouds.
Thunderstorms are of course the most visible and extreme case, where ongoing condensation releases latent heat which prolongs the uplift, allowing the surface convection to reach the stratosphere.
There are also scenarios in which mountain wave turbulence produces alternate bands of clouds, in an atmosphere in which no thermals are present.
So, the answer is, its complicated!