I've got the iPhone SE 2020 with iOS 15.3 and a Logitech K380 Bluetooth keyboard.
Normally, I unlock my iPhone by pressing VO+H then typing my 6-digit passcode. And normally this works fine. However, if there is a notification on the lock screen, the prompt for passcode and number pad do not appear, no matter what keys I press (and I've tried quite a few). The only way to get the passcode prompt is to dismiss the notification first. Then, and only then, will VO+H bring up the passcode prompt.
It's a minor issue, but should probably be listed as a bug with all the other lock screen and notification issues we've been seeing lately.