In terms of numbers I don't know but I personally chose it from my apps and to me it's the best framework out there at the moment.
Compared to the native tech the advantages are easy, you have a single codebase and UI for all the platforms. The native UI apis are also moving faster than Flutter in my opinion which makes Flutter lower maintenance as well on this area.
Compared to React Native, it's younger but more stable in my opinion, I don't want to deal with the js package churn rate and its bad testing story. I come back 6 months after to my flutter projects and after 2 hours I've upgraded everything, good luck with that on the js side.
If you care about Linux, Flutter is also a better choice than React Native in this scenario. React Native Gtk target is abandoned and the only realistic solution is to use an Electron wrapper (well it's not that native anymore isn't it)
The only downside to me is the web target which isn't that great, if you just want to use the web target as an app demo though, it's good enough.