Volume increments do not work
Because of the "surround sound" audio hardware on the UX390, you have to tweak a Pulse configuration file to get volume incrementing to work. Otherwise, the volume will either be full or muted, despite appearing to increment.
Edit the analog output path config and add the
Element Master and
Element LFE parts below.
[Element Master] switch = mute volume = ignore [Element PCM] switch = mute volume = merge override-map.1 = all override-map.2 = all-left,all-right [Element LFE] switch = mute volume = ignore
Then, restart PulseAudio and changing the volume should work.
Headphone jack audio is always muted
Keyboard and Touchpad unusable in X and Wayland
Since kernel version v5.8, the
asus-wmi driver gained the ability to detect "tablet mode" on convertible devices. However, at least on UX390UAK the
asus-wmi driver believes that the device is always in tablet mode, although it is not a convertible (see  for a kernel bug report). Libinput automatically disables touchpad and keyboard when kernel reports tablet mode, so they only work in tty but not in X or wayland.
To workaround this, add a quirk file for libinput:
[test override 1] MatchUdevType=touchpad ModelTabletModeNoSuspend=1 [test override 2] MatchUdevType=keyboard ModelTabletModeNoSuspend=1