Is this a fix for the '-mnative' error on macOS?

No, it's a fix for a deadlock following a call to linux32:

WARNING: The requested image's platform (linux/386) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
3fca67068b8d0aa05202598ccb3d9e80a27327038b85ede10fb6ab3f73b7543e
    + /bin/true
linux32: Failed to set personality to linux32: Invalid argument

I think that the ENTRYPOINT isn't used when you specify a program via run or create?

It's definitely used on run, the program specified via run is passed to the entrypoint. I'll check it's passed via create also and add a test for this.

Turning this into draft until I get time to address all comments.

It's definitely used on run, the program specified via run is passed to the entrypoint. I'll check it's passed via create also and add a test for this.

Ah, perhaps I am confused about the difference between CMD and ENTRYPOINT.

I checked https://docs.docker.com/engine/reference/commandline/create/ and since the ENTRYPOINT can be overridden (same as with run), it's used.
So the confusion might indeed come from ENTRYPOINT vs CMD (which is indeed overriden when specifying a custom command).

Reaching disk space limits once again. I'll add different commits to free some space.

seems cirrus-ci windows x86 is having troubles, found cirruslabs/cirrus-ci-docs#1232

edit: this is now fixed.