I think it's something with the monitor's firmware.
- Does the monitor have its own power button? Does it disconnect the power flow completely?
- If it doesn't, it could be the monitor's firmware misbehaving, thinking the button was pressed when it wasn't.
- When you shut down your computer, see if the monitor turns off as well, or if it stays on and says "No Signal".
- Also, test it with another computer.
Another possibility is with the GPU. Try disabling it temporarily, and booting with only software rendering.
Standard on Debian, hardened on Artix.