As you can see, when you enable blockstate culling, the leaves culling options become grayed out, but they still work when set before disabling blockstate culling (I set the leaves to fast before enabling blockstate culling and it is clearly still working on the 4-layer-deep wall of leaves I am looking at in the screenshot). Could this be fixed?

Ehh I don't think this is caused by me. I think it may be caused by your modified sodium settings.
Can you check if this happens in the default vanilla settings

After checking, this is not a problem with MoreCulling. It's probably an issue with whatever sodium re-skin you are using

Yes, this is on purpose. The leave culling uses that culling system.

this is indeed an issue of this mod, even when I'm not using Reeses sodium options, it is grayed out when the BlockState Culling is toggled: