Has there been any work attempting to not have to run linux on the i.MX 8M Mini of the Portenta X8? I'm developing an application where I have really tight real-time requirements and need quite fast clock speed (the H7 might even be too slow) and can't afford the linux scheduler kicking in from time to time. The project is attempting to do visual-inertial odometry on some embedded platform, where previously this is often done on processors with quite a lot more power. The tight real-time requirements come from the sensor fusion and I need high clock frequency to be able to do the image processing quickly enough to get to a framerate which won't make the odometry diverge. From what I've seen online, and even from NXP, this doesn't seem like there is any support for this. Of course it would be possible with enough time and tinkering, but that reduces the time I've got to spend on the rest of the project (thesis work).
I'm going to assume that it's too early for any viable alternative OS to be available.
I also doubt Arduino will be working on this since it appears https://foundries.io are handling development on the Linux side.
If you manage to port another OS or get code to run on bare metal please do share your findings.
NXP has been working on something similar to your question, it's a real-time edge software release for processors, you might check these links to see if it might help you project.