operating system – Real time OS (RTOS) for Raspberry Pi to make a CNC Controller

this is my first post please be kind.
I have experience programming C++, but it has been a few years since I did anything…

I would like to program a real-time CNC controller, to run CNC machines without a motion controller. I will use a Raspberry Pi and connect it to a MESA card for running all the physical inputs and outputs.

The application and GUI for touch screens will in the future support a small simple slicer for 3D printers, and some simple CAM operations for graphically programming CNC machines for simple tasks.

What RTOS would you recommend to build my program on?

-I have thought about making a Linux based system run realtime, or maybe use Zephyr OS.

Please share your thoughts.

Regards William