What's waking up my card and how can I get it into a powered off state when using On-Demand?

Hey,

I have a Thinkpad with a dedicated RTX 3070 mobile. I am using Ubuntu 21.04 with KDE and in nvidia-settings the system is set to work in the on-demand mode.
Recently I read on reddit that even probing the temperature causes the GPU to be awake. The power state can be checked in /sys/bus/pci/devices/0000\:01\:00.0/power_state and it always says D0, even after I have removed the sensor from the KDE widget that shows the temperature in the system tray.
Furthermore, nvidia-smi reports a process that is always running:

+-----------------------------------------------------------------------------+
| Processes:                                                                  |
|  GPU   GI   CI        PID   Type   Process name                  GPU Memory |
|        ID   ID                                                   Usage      |
|=============================================================================|
|    0   N/A  N/A   1027686      G   /usr/lib/xorg/Xorg                  4MiB |
+-----------------------------------------------------------------------------+

I am not sure whether this affects the power state.

How can I figure out what’s keeping my card awake and how I can turn it off when I don’t need it?

[edit]
Even after shutting down the X server via systemctl stop sddm.service it still reported the power state as D0. Might that be an issue with the driver?