If your workspace fails to start in a project that has an external github repo attached, please check for the following error in the User logs:
2021-08-25 03:53:13 : Critical error in run 61269ef108817c6c5dd83db4: org.eclipse.jgit.api.errors.TransportException: https://<domino-url>/<username>/<project-name>: git-upload-pack not permitted on 'https://<github-url>/<username>/<repo>/'
The User logs will be in different areas of the UI depending on your version of Domino. You will be able to find them under the Logs menu of the workspace, or in the workspace History menu.
This "git-upload-pack not permitted on" error is reported to have multiple causes, but has been resolved in some instances by ensuring that your personal access token has the permissions required to access the attached repo in Github.
If the required permissions are in place and workspaces continue to fail with this error, please grab the support bundle from your workspace and engage Domino support for further assistance