Take a look at the decade+ long effort that Debian has put into this problem: https://wiki.debian.org/ReproducibleBuilds
Here's a talk from 2024: https://debconf24.debconf.org/talks/18-reproducible-builds-t...
Several distros are above the 90% mark of all packages being byte-for-byte reproducible, and one or two have hit the 99% mark.