Figure out what physics says about the physical footprint of say 10 million small hominids who want to remain alive but live life entirely in virtual reality pods. I think you’ll conclude that from first principles you can say very well hidden, have a sustained existence as long as you fix the population, if you solve the engineering problems of situating your hardware in a void in the ground. Particularly if you know a priori you only need to do it for a few millennia.