HDMI outputs appears as “unavailable”, but running aplay command, it plays!

Motherboard: AMD Rs780
System version:

uname -a
Linux UBUNTU-2020 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020  x86_64 x86_64 x86_64 GNU/Linux

On pavucontrol => Configuration, all HDMI outputs appear as “(unavailable)”

Listing the HW Devices:

aplay -l

**** List of PLAYBACK Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: ALC887-VD Analog [ALC887-VD Analog]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 1: ALC887-VD Digital [ALC887-VD Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: HDMI [HDA ATI HDMI], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

If I run this command, the sound flows through HDMI!

aplay -D plughw:1,3 /usr/share/sounds/alsa/Front_Center.wav

This command also works:

speaker-test --channels 2 --rate 48000 --device hw:1,3

I’ve tried to change /etc/asound.conf like this:

defaults.pcm.card 1
defaults.pcm.device 3

The HDMI then appears as an output device, but no sound. If I run the aplay command again, it does not play anymore:

aplay -D plughw:1,3 /usr/share/sounds/alsa/Front_Center.wav
aplay: main:830: audio open error: Device or resource busy

Any thoughts?

Thanks!