Implement a "Pass-Through" blending mode specialized for Folders in the LayerStack.
"Pass-Through" differs from "Normal", as it will act as if there is no temporary/intermediate Folder Block to hold the merged content of the folder, before blending it in the result block, instead, the layers contained in the folder are directly blent on the result. This allows for the blocks of the folder to apply their blending mode on the underlying result for certain translucency effects, while retaining the possibility to have them grouped.
See https://community.adobe.com/t5/photoshop-ecosystem-discussions/pass-through-blending-option/m-p/9259865 for equivalent option in Photoshop.
This blending mode has to be handled as a special case as it is only relevant for Folders.