So, for slickytail and anyone who has the same question:

The code is actually compressed into a binary blob. You can see it if you just look at the source of https://0b5vr.com/0mix/0mix.html

A small script loads the blob and uncompresses it before running it through eval:

  fetch("#").then(t=>t.blob()).then(t=>new Response(t.slice(156).stream().pipeThrough(new DecompressionStream("deflate"))).text()).then(eval)