You can find the API key screen under Settings -> Development -> API Keys.
To create a new API key, click the "CREATE API KEY" button in the upper right corner. Give the API key a descriptive name, such as the name of the environment variable in your project. A modal will appear, displaying the newly generated API key.
After entering the name, you will receive the API key, which you can copy and save for later use in your project.
Please note that once you close the modal, you won't be able to access the API key again, so it's important to copy and store it securely. If you lose the key, you can only delete it and generate a new one.
With the API key, only operations in the external API are allowed. The key only provides access to the single project where it exists. If you have no blueprints that have mutations enabled, your API key can only read data from the external API, nothing more.