If string theory is implausible could the most fundamental substance still be vibes? Why? How? Yes because vibes are not strings.Source: Thesis The Arche May be Vibrations
Yes, fields of vibes or oscillations (perturbations of something like a medium or spacetime) are very likely to be fundamental in quantum theories and gravity. I think that the key to solve these problems is purely geometry. See for instance the embedding of our universe in a five dimensional Minkowski space, that can explain the Hubble tension and the MOND behaviour by perturbing reference frames (fictitious acceleration):