Not really, actually.

At an intentionally vague high level: The main components of a firearm are:

1. The frame
2. Levers/internal bits
3. The barrel
4. Metal springs and wires to connect the internal bits and make semi/full automatic fire possible
5. The firing pin

1 and 2 are 100% able to be made with plastic. And that is increasingly becoming a selling point for a lot of firearms because of “weight”

4 is trivial to pick up at any hardware store and isn’t even conspicuous.

Which leaves 3 and 5. Plastic/polymer barrels are not an issue for small caliber ammunition (e.g. pistol rounds). You just don’t want to use dirt cheap PLA for that. And probably futz with the infill settings a bit.

The firing pin: Most engineering analyses I have seen say that is the one part that needs to be “real” (and, thus, is a traceable purchase). But I’ve seen a few resources tiptoe around how this could be easily improvised from stuff you buy at the local hardware store. And if I cared enough to check The Dark Web, I am certain I could find step by step instructions on how to do exactly that.

And there are youtubers like Emily the Engineer who have made it a point to show how ridiculously strong 3d printed stuff is. She doesn’t do firearms (mostly because it would get her demonetized…) but 3d printed machetes, lawnmower blades, jacks for pick up trucks, etc are pretty trivial. And I would be pretty shocked if someone who was had a particularly well configured printer and some of the good plastic couldn’t make a (mostly, if not entirely) polymer firing pin (I actually have no idea how modern ammunition works. I THINK it is just compression of the charge which means no metal needed. But if you still need a spark of some form, that is a metal tip instead of a metal pin).