[1.17.1] How can i skip render of one face of a Block

[samjviana]

I asked before, but didn't get any responses
I have an custom slime block that works exactly the same as the vanilla one, but it is visually different. The thing is, the vanilla block, don't render the face that is in contact with another block os same instance, i assume that the function HalfTransparentBlock$skipRendering is responsable for that. To make my block i just extended the SlimeBlock class but the render of the face keep getting rendered, i even override the skipRendering, but it is never called.
Here's an screenshot: (left: modded slime block, right: vanilla's)