Never mind - I figured it out
I checked some posts and found out that I have done this (pretty long ago):
Clone all from the habpanel web folder from github into html/habpanel (you’ll have app, assets, fonts etc. then in the html/habpanel directory)
https://github.com/openhab/org.openhab.ui.habpanel
You won’t see the new icons until you use the static-URL: http://your-openhab-server:8080/static/habpanel/index.html
I did not remember, that my (old) habpanel placed on my homescreen hadhardcoded the static html liked.
That’s why it did not show the right itemState because I was actually running the old habpanel, not the one coming with OH 2.1.
After cloning the web folder from habpanel into my /etc/openhab2/html/habpanel including the icons I have added to my previous (old) habpanel, everything works as expected.
Thank you!