Does gmail use the Seen flag?

[tinmac]

Im setting Seen flag like this

var folder = await client.GetFolderAsync(f_uid.FolderFullName);

await folder.OpenAsync(FolderAccess.ReadWrite);

if (Seen == true)
{
    folder.AddFlags(f_uid.Uids, MessageFlags.Seen, true);
}
else
{
    folder.RemoveFlags(f_uid.Uids, MessageFlags.Seen, true);
}

The flags do indeed change as I get the Idle notifications showing as Seen.

However if I load up Gmail in chrome browser and select the Inbox, the email in question retains its bold style as if it has not been read, I was expecting it to be styled normal ie non bold (ive tried to hit the refresh button too but still bold).

So now im thinking Gmail doesn't use the Seen flag in house and maybe they have another mechanism?

My goal is to mark as seen in my email client and for that to sync through to other gmail clients, is that possible?

EDIT : gmail does use the seen flag to apply the bold styling. I had a conversation thread with some messages marked as seen and some not, once all were marked then the all appeared as expected.