The Survey123 connector is available in Microsoft Flow. You should be able to use 'Create from blank', 'Search from hundreds of connectors and triggers' and type in Survey123 and see it in the results:
Below is a screenshot of what I see when searching for the Survey123 connector. Are there any additional steps required to access the connector that are not listed in this set up page: https://community.esri.com/groups/survey123/blog/2018/07/19/automating-workflows-with-survey123-and-... ?
I keep having the same issue as Megan, with no Survey123 connector when I search for it under 'add a trigger'. Is there something else that we need to configure to access it?