It seems that the Volar and TypeScript Vue Plugin have moved to the vue publisher ID in the VS Code marketplace where they previously were johnsoncodehk. They still are johnsoncodehk in the package.json of the version that currently gets installed (Guess they weren't released since the rename), but that no longer works in extensions.json to recommend them and it should now be:

"vue.volar", "vue.vscode-typescript-vue-plugin"