There is some problem in the Clipping Plane Feature Page https://doc.babylonjs.com/features/featuresDeepDive/scene/clipPlanes
It says:
Since version 5.0, the best way to use clip planes in this case is through the properties
material.clipPlane/clipPlane2/ … /clipPlane6. This way, you don’t need to add observers toonBeforeRenderObservable/onAfterRenderObservable.
It Should be:
Since version 5.33.0, the best way to use clip planes in this case is through the properties
material.clipPlane/clipPlane2/ … /clipPlane6. This way, you don’t need to add observers toonBeforeRenderObservable/onAfterRenderObservable.
Ref: https://github.com/BabylonJS/Babylon.js/commit/3cd0d09caec8e8a7bfc2f6df3ad69e46d97c0fb1