Indeed, you are right and obviously I was simply too stupid to know that Google Home is mandatory for initially setting up a Chromecast receiver device.
After doing a factory reset, my phone detected the 1120 and asked me if I wanted to set it up as a Chromecast device. Yes, I do (I don't remember having seen this in my first setup attempt). Only when I was redirected to Play Store to install Google Home, some past memory stroke me ...
I bought an Onkyo R-N855 about two years ago and yes, back then I
did install Google Home. However, since I'm not really interested all this home automation stuff, I later uninstalled the app. The Onkyo R-N855 continued working with Chromecast (it never worked particularly smooth), so I completely forgot about this.
Now, on to new adventures. I never really figured, if and how Chromecast still works with ethernet connection, only. I'll probably find out.
One thing I can say for sure - leaving all this devilish black streaming magic aside: I really love the phono MM input. Extremely quiet. Extremely detailed. Extremely neutral. Those running multi-k bucks valve pre-amps won't take me seriously anyway, because so far I was more than happy with the build-in phono pre on my (heavily pimped) Quad 34. But I do feel that the 1120 does in fact better this.