There are two ways of installing meld on osx (May 2023), using brew and .dmg package (from @yousseb). Since I found https://yousseb.github.io/meld/, I've installed it with .dmg package, but having macOS Ventura Version 13.4 (22F66) in place, it's not even starting for me. So I tried brew installation, and the application is working as expected, including symlink to start it from the terminal.
Using brew formulae: https://formulae.brew.sh/cask/meld
brew install --cask meld
# set meld as your default git mergetool