Workspaces seem temporarily broken, see here. Could that be part of the issue for why trying that approach isn’t working?
UPDATE: Maybe workspaces work via MyBinder sessions if you try on a fresh machine or in fresh browser? See discussion going forward from here. So maybe linking to notebooks not broken? There is a caveat about the current ‘Try Jupyter’ JupyterLab example not working with the work-around or solutions that have worked elsewhere to resemble a fresh launch, see the ‘Caveat’ description here, which may suggest it is JupyterLab 3 or specific versions of JupyterLab 3 that do indeed have workspace issues.