Nope, works on non-rooted phones too. There’a a new installation framework in recent Android versions that allows background installs by apps other than the Play Store!
I actually have a friend that uses such a small phone, they use a regular querty keyboard, just usually in combination with glide/swipe typing. I don’t think you can install WearOS keyboards, and afaik the default keyboard on WearOS is a full-size querty anyway…
I also get that oversharpening effect on my Zenfone 10 :(