It appears to be nearly non-existent. Project page claims that it supports 58 devices, but for example, Redmi 7 is listed at 9th place and fingerprint sensor doesn't work on it. https://devices.ubuntu-touch.io/
I really cant imagine this is a good use of resources, barely anybody uses ubuntu touch anymore. Supporting it as a build target seems like a bad idea based on that alone.
It would be nice to have a serious alternative to Android and IOS. But it would have to be so accessible anyone could install it, or acquire it from a store. Also, the hardcore Linux people rarely pay money for software or games as far as I know.
Linux users can normally recognize value of software, but a "linux for cellphones" would need a backing of a corp. And that's why it won't be a thing. "Slackware: Mobile Edition" could fun, though. Although there's also a question whether traditional gnu/linux stack even makes a lot of sense on a mobile OS.