So I wanted to have more than 8 morph target to be activated for certain kinds of meshes as it is an requirement. I know that threejs limits the number of morph targets to 8 which is also the limit of webg2 .
Then I came across this unique solution by Francois-Laberge-Bose :
Locally I tried to change the webgl_morphtargets_horse.html from threejs examples and convert it for the sake of the demo : webgl_morphtargets_horse.html (9.5 KB)
I think I found the solution to this cube at least right now , you need to set the shader with the exact number of morph influences you have instead of what the author set (63)