External monitor waking up both displays when going standby during locking

Hi guys, have a problem with screen after locking. I have laptop with main screen and external display connect via HDMI. When I lock the GNOME both screens going to ‘standby’, but than after few seconds second screen display messages ‘no signal’ and than ‘entering power saving mode’ and this action turn on both screens: they black but still on (meaning not in standby mode).

Do you have any ideas how fix it?

What are the GPUs?

If you have the nvidia GPU it can cause this since by default the nvidia GPU drives the hdmi port and the IGP drives the built in screen so some have the same issue you are seeing.

Searching this forum for problems with suspend gives several potential fixes.

AMD Vega 3 (Picasso)

Same situation when screen goes blank after time interval. Both displays stay blank than external goes to ‘powersaving mode’ and awake both. Cyclic situation.

I think I need to customization way to configure events to prevent interruption.

I think I said it wrong in that last post. IGP and discrete GPU should have been what I said, since it is not limited to nvidia.

Can you by chance show us the output of

inxi -Gxx 

so we can see the actual graphics hardware config and drivers.

  Device-1: AMD Picasso vendor: Lenovo driver: amdgpu v: kernel 
  bus-ID: 04:00.0 chip-ID: 1002:15d8 
  Device-2: Acer Integrated Camera type: USB driver: uvcvideo bus-ID: 1-1:2 
  chip-ID: 5986:1135 
  Display: wayland server: X.Org compositor: gnome-shell driver: 
  loaded: amdgpu,ati unloaded: fbdev,modesetting,vesa 
  resolution: 1536x864~60Hz s-dpi: 96 
  OpenGL: renderer: AMD Radeon Vega 3 Graphics (RAVEN2 DRM 3.42.0 
  5.14.14-200.fc34.x86_64 LLVM 12.0.1) 
  v: 4.6 Mesa 21.1.8 direct render: Yes 

The only thing I can think of from that is you are using wayland.
Have you tried using xorg to see if the fault is wayland by chance?

If not, then please do. It is possible the issue is in wayland itself and trying xorg would help narrow down the cause. If it still occurs in xorg then it is a little deeper.