PlantUML extension for Visual Studio Code on Windows only working with sequence diagrams

The GRAPHVIZ_DOT environment variable is specified in File > Preferences > Settings > Plantuml: Command Args. Click on the link to "Edit in settings.json".

Additionally the VSCode PlantUML extension doesn't appear to include the graphviz "dot.exe" executable, so this needs to be downloaded and installed (e.g. via chocolatey OR download and unzip from https://graphviz.gitlab.io/_pages/Download/Download_windows.html)

Following this, update the path and save.

{
    "plantuml.commandArgs": [
        "-DGRAPHVIZ_DOT=D:\\Tools\\graphviz-2.38\\release\\bin\\dot.exe",
    ]
}

Also see https://github.com/qjebbs/vscode-plantuml/issues/94