I was hoping someone who actually uses macos would address this, but given nobody has I've had a go myself.
It's hard to be sure because only the end of the log is shown (whereas typically it's the first errors that are the most interesting) but my guess was that this is a proj version issue, so I've updated the homebrew repo to Survex 1.4.1 which works with newer proj versions.
I have also managed to set up test installing via continuous integration so this new package should install on both macos 10.15 and 11:
https://github.com/ojwb/homebrew-survex/actions/runs/1781622178
I'll close as this should be resolved - if it isn't for you please reopen (or comment if you can't and I'll reopen) with details.