Sorry, not an answer, but I'm also curious about this topic.
I've had really good experiences using Manjaro and KDE on personal devices for a while now. It's my go to ecosystem, but more out of personal preference than objective criteria. One of the appeals of the PinePhone (when I had one) was that it could function as an extension of that world. If the x23 got to the point where I could have the "ability to reliably be a phone" that comes from the android base vollaOS but also dual boot to a compatible mini computer that would be ideal for me (but again that's just the environment I find most comfortable).
That said, I've also (begrudgingly) kept a Ubuntu laptop around for interacting with the "wider world" when needed. I don't know to what extent UbuntuTouch works within that. If I could have all of my minimal mainstream needs meet by a combination of best case compromises (de-googled Android for phone and Ubuntu for interacting with software/drivers that don't play nice with arch) dumped into one portable, external device I would be very satisfied. My impression though is that UbuntuTouch is more about making Linux work as a phone than putting Ubuntu onto a portable device, but that isn't based on experience. Interested in being corrected.