Currently it's only possible to use delegate permissions to get chat lists, some requests need a signed in user to be able to fetch the information.
List chats - Microsoft Graph v1.0 | Microsoft Docs
But we have some business tasks that require to get a list of user chats for statistics. Obviously, only general information: id, chat members, start datetime, last update datetime.
I 'm sure it would be a useful improvement for developers.
So please, consider an option to get a list of chats for an application user