Does anyone know of a workaround to this bug for Survey123?
The status of Esri BUG-000120809 - Survey123 for ArcGIS web app does not allow Portal for ArcGIS users accessing a survey link to be prompted for sign in when Portal for ArcGIS is configured with Integrated Windows Authentication (IWA). - that you have been associated with has been changed to Not in Current Product Plan.
Public Explanation: Currently, when attempting to access a survey that has been shared from an IWA Portal using a share url in the following format...https://survey123.arcgis.com/share/<itemid>?portalUrl=<portal>/portal the submitter is directed to a page stating "The survey does not exist or is not accessible."
In the top right corner, there is an option to 'Sign In'.
After selecting this, the submitter is redirected to a Sign In dialogue to authenticate with their IWA credentials. After doing so, the survey can be accessed successfully.