Using the GetTotalUnreadChannelCount() method, you can retrieve the total number of group channels in which a user has one or more unread messages.
SbGroupChannelTotalUnreadMessageCountParams unreadMessageCountParams = new SbGroupChannelTotalUnreadMessageCountParams();
SendbirdChat.GroupChannel.GetTotalUnreadChannelCount(unreadMessageCountParams, (inCount, inError) =>
{
if (inError != null)
return; // Handle error.
// Further processing using inCount if needed.
});