I'm genuinely curious how you've determined that "most activity" is on CircuitPython? I'm close to both projects and they are both highly active. MicroPython tends to be lower-level and a little more under-the-radar, especially since Adafruit provides such a focal point to CircuitPython (and do a great job with it!).

As for libraries; there's a whole lot of MicroPython libs listed on awesome-micropython.com and, if you need to use a CP library in MP, it's often trivial to port.

I was a little surprised to see MicroPython mentioned at all here since there's not really much that Ubuntu is doing to provide that support. I guess it was to refer to the popular RPi Pico, which has official support with MicroPython. CircuitPython support is becoming very close to parity on the Pico though.

(I'm not sure what you mean wrt UF2 on ESP32-S2; it has always worked fine for me? I just tried it again and there were no issues. Note that - unlike the Pico - the UF2 bootloader is not in ROM so you have to install it first.)