Thank you, I found it!
But I don't know what to put into "PoseStack", "MultibufferSource" and a float[], rn I have assigned random Values which crash my game...
BeaconRenderer.renderBeaconBeam(new PoseStack(), MultiBufferSource.immediate(new BufferBuilder(30)),BEAM_LOCATION, 5, 5, 5, 5, 5,new float[5], 5, 5);
the other values are probably just color and locationg, I think I can get them right with try and error ^^