What I would have done is tested it with an Android phone. My Samsung S26 Ultra allows me to connect to an external display via a USB C hub. So the test setup would be:
1. Plug the phone into hub.
2. Check that you get display output, the mouse and keyboard are working whilst the screen is not turned off and the phone is not locked.
3. Lock the screen and wait for the screen to turn off, thereby mimicking suspend.
4. Try to make the phone resume by using the attached keyboard and/or mouse.
If all goes well, the monitor should turn on after unlocking the phone or using the keyboard / mouse.
# Other things to try
Again try and reproduce the issue with a Samsung tablet that supports display out via USB C.
Connect the keyboard via Bluetooth and try to make the laptop resume. I found that connecting a Keychron keyboard via bluetooth allowed me to resume a Macbook Pro. I was kinda surprised that this worked.
Does the same issue occur on Linux as well?
I guess you could attach a USB packet type of debugger to ensure that data is being sent to the laptop by attaching the debugger to the cable that connects to the host machine. If you see USB traffic when the monitor goes to sleep and you are pressing keys in the keyboard and the dock still has power that means the dock is working fine so you can rule that out.
1. Plug the phone into hub.
2. Check that you get display output, the mouse and keyboard are working whilst the screen is not turned off and the phone is not locked.
3. Lock the screen and wait for the screen to turn off, thereby mimicking suspend.
4. Try to make the phone resume by using the attached keyboard and/or mouse.
If all goes well, the monitor should turn on after unlocking the phone or using the keyboard / mouse.
# Other things to try
Again try and reproduce the issue with a Samsung tablet that supports display out via USB C.
Connect the keyboard via Bluetooth and try to make the laptop resume. I found that connecting a Keychron keyboard via bluetooth allowed me to resume a Macbook Pro. I was kinda surprised that this worked.
Does the same issue occur on Linux as well?
I guess you could attach a USB packet type of debugger to ensure that data is being sent to the laptop by attaching the debugger to the cable that connects to the host machine. If you see USB traffic when the monitor goes to sleep and you are pressing keys in the keyboard and the dock still has power that means the dock is working fine so you can rule that out.