Documentation around PlantUML and how to setup (especially when you don't typically work in Java) leave a lot to be desired. Here's a quick run down of how to get plantuml setup and running so you can create, edit, preview and export the diagrams (including C4 Model) in VS Code.
First, ensure you have homebrew installed and updated: https://brew.sh/.
Install the temurin
JDK, graphviz
and plantuml
in that order.
brew install --cask temurin