Papers have been published that have found ways to create warp drives without the need for exotic matter: https://arxiv.org/pdf/2006.07125.pdf

I know, I was making reference to this

> They are only theoretically possible if you allow for negative mass and energy--not an engineering problem so much as a "need to find exotic matter"

Basically people ran the EFE "backwards" to see what matter distribution makes the wanted curvature. You get either negative mass-energy or the bubble doesn't travel ftl iirc.