Thank you, Vaibhav, for your response. You put me on the right path!
When setting up the GitHub Action during the process of establishing an Azure Static Web App, you are asked for app, api, and output locations.
As a test, I created a standard create-react-app app without the client/server folder structure of my current app. The GitHub Action was able to install, build, and deploy my Static Web App on Azure with no problems.
I then went back to my current app and changed the three locations to be:
app_location: "client" # App source code path
api_location: "server" # Api source code path - optional
output_location: "client/build" # Built app content directory - optional
The deployment still failed. But it failed for a different reason than before. Progress!
I then got this error: "The app build failed to produce artifact folder: 'client/build'. Please ensure this property is configured correctly in your workflow file."
Following the advice of this Stackflow thread (https://stackoverflow.com/questions/64155765/react-js-deployment-with-github-actions-workflow-to-azure-web-app-build-folder-i), I changed the output location to just "build" but left the other two locations as they were.
And now the GitHub Action successfully deploys to Azure Static Web Apps with with a client/server folder structure.
Thank you again for your help,
Travis