It doesn't seem like the proj problem is connected to the final failure, but I'm not sure what's causing either.
You could try updating again, as I see wxmac got updated to 3.1.5 2 days ago:
https://github.com/Homebrew/homebrew-core/commits/46ad714cc4d3140b69723b7bfc0395f085b642b9/Formula/wxmac.rb
Maybe 3.1.5 supports the latest macos better.
If that doesn't help, I don't have a mac myself so it's hard for me to investigate, but we can see if Robert Jones can take a look (he put together the homebrew packaging).
