On my Huawei Mate 10 with Android 7.0 and a test app with SDK 26 and 27 the legacy notifications still work. As I've understood, they should not work anymore:
Dim n As Notification
n.Initialize
n.Icon = "icon"
n.OnGoingEvent=False
n.Light=True
n.SetInfo2("FCM","Message sent: " & MyData.get("time"),"This is the tag", "Main")
n.Vibrate=False
n.Notify(1)