looks like there´s light at the end of the tunnel… 
I got inspired by @RD138 No mobile data connection on S7 edge - #5 by RD138
Other than in his solution/description there was no proxy defined in my APN-settings that I could delete… but I doublechecked the recommended APN-settings for S7 at my providers support-page (congstar). There is only recommendations for Android 6+7 available but in terms of APN-settings they are the same.
So I tried and changed APN from “internet.telekom” to “internet.v6.telekom” as specified by congstar and left all other settings untouched.
et voilá: mobile data available again for e.g. signal-app…
The other apps and websites seem to have access to internet via mobile data as well!
As of now I can say that only app-lounge still crashes often (but after a few restarts at least has internet access via mobile data). There must be some other issue with that app that has little or nothing to do with mobile data…
I recommend to doublecheck APN-settings if mobile data access on V1.0 is an issue. It´s worth the try as it seems 
edits: clarifications