I feel like nihilism only survives because of a blindspot. Like if you are really that worried about the idea that maybe nothing matters, that means something does matter to you. I don't think things can stop mattering to people. I feel like it's an axiom ingrained in our biology. Things matter to us, and it's not our choice. To find what matters just ask yourself "what do I want?". And then to the answer of that question ask "why do I want that?" And then keep asking that to each answer until you come to the point where you have no answer as to why you want it, it's just a feeling that you want it, and it's beyond you. Then that must be the axiom ingrained in your biology. And that's what matters to you.