Thanks, you gave me the keyword I needed to find the answer here in the forum.
As I read, Ubuntu Touch on Volla Phone uses Halium. And when searching for “Halium” here in the forum, I found this answer of @spikerguy, that Manjaro ARM via Halium is currently being tested, but in a very early stage.
About what I am expecting: it does not need to be a completely Android-free Phone/OS. For me it’s more important, that there are usable alternatives to (“Google”-)Android. Also I was not expecting a finished OS, yet. And I am willing to help with testing.
Thanks again 