Something like this maybe:
https://travelerguitar.com/all-models/
https://travelerguitar.com/speedster-red/
I just shipped off a Speedster yesterday that has been living in my closet for years. But even this is 27-30" long in its gig bag, depending on the model.
A Martin Backpacker, while not much of a guitar, can be an acceptable practice tool on the road. Their web site doesn't list the overall length, but looking at the pictures, I would guess about 32".
After that you are into a ukulele of some flavor, be it baritone, tenor, or Guitalele.