If one could cross compile to something like an ARM-Cortex, 5k hello world with no GC would be very interesting.

I assume you mean an ARM microcontroller? I think it may be possible. .NET has a code generator for ARM32, which I think generates Thumb-2 instructions.

The trouble I had last time I tried (.NET Core 3.1 I think) is you needed a cross compiling versio of RyuJIT that has the same bitness of your target. That is , you needed one that ran on linux x86 targeting linux arm32. And that was not easy to find. Maybe if I try compiling from a Arm32 host it will be easier.

I’m not sure it would because a C one is measured in bytes and does the same thing.