I rebooted into Eoan's 5.3.0-29.31 kernel, with Focal's userspace, and verified that the screen brightness is still adjustable under that kernel. Additionally, it is worth noting that I saw the same "hp_wmi: Unknown event_id" warnings mentioned in comment 2 so they probably don't have anything to do with this bug.
I rebooted into Eoan's 5.3.0-29.31 kernel, with Focal's userspace, and verified that the screen brightness is still adjustable under that kernel. Additionally, it is worth noting that I saw the same "hp_wmi: Unknown event_id" warnings mentioned in comment 2 so they probably don't have anything to do with this bug.