J C Paul
Hi there,
1. As per my guess, you're using ‘Don't show notifications at all’. Well check that by heading to Settings – Apps & notifications – Notifications – On lock screen. If this option is set to ‘Don't show notifications at all’, Ambient display won't make the screen wake. Set it to either ‘Hide sensitive content’ (the screen will hide all messages; it'll display only the apps) or ‘Show all notification content’.
2. For using Screen saver, you'll have to leave the screen on; it won't work if you lock the screen. Select your preferred time and get the most of this feature.

it's just a bug because i have chosen to show nofication in lockscreen but same "not work"