View Source ExTDLib.Method.GetSuitableDiscussionChats (ExTDLib v0.0.4)

Returns a list of basic group and supergroup chats, which can be used as a discussion group for a channel. Returned basic group chats must be first upgraded to supergroups before they can be set as a discussion group. To set a returned supergroup as a discussion group, access to its old messages must be enabled using toggleSupergroupIsAllHistoryAvailable first. Returns object_ptr<Chats>.

More details on telegram's documentation.