Google Drive provides an option that anyone with a link can view, and this is exactly what I need in this case.
The client is in government, so them getting their own viewer account is not an option. That map contains government data and can not be made public.
This question has been asked before without an answer:
https://community.esri.com/t5/arcgis-online-questions/how-do-i-give-a-client-access-to-a-web-map-wit...
Thanks!
I don't think this is currently available in ArcGIS Online. If you want the content to actually be secured, you will have to avoid sharing with everyone. Many government agencies have ArcGIS Online accounts and even their own Organization pages. If that is the case, you can set up a collaboration between your orgs and share the content that way.
If you want to vote for the functionality you mentioned, check the Ideas page for an existing idea that explains the same functionality and vote for it. If it does not exist, you can create one yourself.