Is there a stereo input USB C ‘dongle’ yet, or anything really small?

[jemmons]

Again, the Apple USB-C to 3.5 dongle you suggest only supports TRRS. TRRS has left-out on the tip, right-out on the first ring, and a single audio-in on the last ring.

That’s only a single channel in. No stereo.

So it doesn’t provide any advantage over the built-in headphone port of the OP’s MacBook. That supports TRRS already on its own.