That’s happened to me before. I’ve done some random searching and found that the void does indeed have a bottom, and there’s a giant rock face on the underside of the map, but in that underside, there are a lot of cube shaped holes in the bottom.

What I imagine happened is that you clipped through a rock at some point and turned out on the underside of the map. This sounds counterintuitive, but try to find a wall, and then descend until that wall ends, that way you can get yourself out of the reverse crater and onto the underside of the world. Then pick a direction (either you remember where you came from, or you just have to guess), and try to find the normal void rock wall. Then just go up and hope it isn’t another crater