According to the documentation on 'How to Add a "Deploy to DigitalOcean" Button to Your Repository' (, we can set placeholder values for environment variables, and those values should be editable during the app creation time (including secrets): "DB_FOO_1 is a secret with a default value, DB-password-testvalue. App Platform lets you edit this environment variable at app creation time."
But variables defined as secret cannot be edited during the deployment of a new app, they have to be deleted an re-added. I even tried removing the value parameter from a secret variable in the template, but it didn't help. It would be extremely handy to be able to set the secret variables values during the initial app deployment.