Still based on the Ubuntu 16.04 LTS (Xenial Xerus) operating system series, Ubuntu Touch OTA-20 is a maintenance update that introduces support for the notification LED and vibration for incoming notifications on Halium 9 devices, such as OnePlus 6, OnePlus 6T, Xiaomi Mi A2, Xiaomi Mi 6, and others.
However, the devs note the fact that some recent devices with a Halium 9 base do not have a notification LED, so this new feature doesn’t apply to them. These include the Volla Phone and Google Pixel 3a.