QNX is not open source.

And seL4 is a kernel, not an OS. And it pretty hard to work with specially if you want any kind of dynamic system.

There is Genode, which can run atop of seL4(amongst others).

https://genode.org/

https://genodians.org/

https://en.wikipedia.org/wiki/Genode

What did you mean by a dynamic system ?

One where processes, drivers and libraries come and go during the whole OS uptime.