It wasn't my best talk (juggling lots of hardware issues with very little sleep!), but "Extending MicroPython: Using C for good!" from PyCon AU 2019 did discuss using native modules (ie written in C but loaded at runtime) with an example to generate QR codes!

https://www.youtube.com/watch?v=437CZBnK8vI

I have a gist that wraps up the Project Nayuki C QR code generator. It shouldn't take too much effort to reuse this if you want a solution that performs much better than a pure MicroPython implementation and is still convenient to load/use:

https://gist.github.com/mattytrentini/09885f5aae78590e5d4cce15a18c62dc