Specification Attribute filtering not working for "Group" products NC4.00

I noticed that, after adding grouped products to my site, the specification filters do not display in the appropriate category (I just see the Sort Order and page size, no filters).
I'm using the Default Clean stock theme for NopCommerce 4.

I've basically have a Grouped product that has the product and a product sample.
I've tried just adding the Specification Attributes to the respective grouped products, that didn't work, so I added the same Specification Attributes to the simple products as well. That didn't work either.

Does the stock product filter not work with grouped products?

Anyone? Is this not supported?

If not, is there any 3rd party plugin that does support grouped products? I've tried all the "free" ones and they have bugs like duplicated Add To Cart buttons or just plain don't work.
Gladly pay for a plugin that will work!!!