Is there a way to limit the cart contents to one very specific item? That, this one item can only be purchased alone?

With a bunch of scripting, sure

Haha, I was hoping that wasn't going to be the answer...

Ha. Well, yeah, "only allow one item in the cart" is not really a use case I've heard before 😅

Yeah, sort of an odd ask...We have a circumstance where we need a non-inventory item that needs free shipping, but we don't want free shipping on the whole cart if they add something else...

We've run into this limitation before, where free shipping on one item makes the entire order ship free.