chatting w/ @nrobinson2000 over the weekend, it seems the issue he was hitting was a result of having used the CLI to create his project (via particle project create).
projects created this way will need to be imported to work with Workbench - within VSCode, run the Particle: Import Project command and follow the prompts. if you are starting a new project that you aim to work on with Particle Workbench, the best approach is the run the Particle: Create New Project command within VSCode / Workbench as this ensures the required ./.vscode files are created and available 