I got it to work!
Activate the cam in dietpi-cpnfig.
Then we need libcamera-tools it comes withlibcamerify.
If you want to test if your camera is recognized, you can also install libcamera-apps
apt install libcamera-tools libcamera-apps
rpicam-hello --list-cameras
This should output the connected cams.
Then we need to change the service file for motioneye:
nano /etc/systemd/system/motioneye.service
You just need to add the this /usr/bin/libcamerify to the ExecStart= before anything else, like:
ExecStart=/usr/bin/libcamerify /usr/local/bin/meyectl startserver -c /etc/motioneye/motioneye.conf
Save the file, and restart the service:
systemctl daemon-reload
systemctl restart motioneye