Hey Ralf,
I highly recommend using the Helm charts.
If using the manifests, you need to set the image tag properly. I will change that on Monday for the 1.0.0 branch. When pulling from main, you will always have to set it.
Currently, it is: checkmk/kubernetes-collector:main_<YYYY.MM.DD>
I recommend using checkmk/kubernetes-collector:1.0.0-beta.1
You have to adapt it for all the other images as well (you can save yourself a lot of work, if you use the Helm charts).