I installed Rust and rust-analyzer from Homebrew, thinking they would work like when I did that on my Windows computer with Chocolatey. The difference is that, Windows apps will inherit environment variables from explorer, but macOS apps will only have a barebones default from launchd. Even if I configure a new PATH entry for homebrew bin directories in /etc/paths.d/, it will not be applied to applications. Apparently, you can manually specify the executable of the LS in Kate, but rust-analyzer will call cargo for its works, and because Kate didn't inherit the PATH environments, cargo won't launch.

This hugely affects Kate's LSP support since installing an LS with Homebrew on macOS is pretty common. I'm not sure what can I do to make it usable.

On Debian I override global LSP client settings by providing my own in $HOME/.config/kate/lspclient/settings.json

Never tried with Rust and/or macOS but maybe it helps...