64 bits.

This is how I used RT-Thread ENV to build for Raspberry Pi 4:
https://youtu.be/Gz9amRmX0DY

I figured it out with the help of the above two answers. I did not make a proper Raspbian image on my SD card hence did not have a FAT32 partition named boot. It is in this readable partition the config.txt exists. This video shows what I did to resolve:
https://youtu.be/Gz9amRmX0DY

raspberry #raspberrypi #raspberrypi4 #raspberrypico #rapi #rapi4 #embedded #rtos #rtthread #rt-thread

I made a video of what I did to resolve for others to follow:
https://youtu.be/Gz9amRmX0DY

raspberry #raspberrypi #raspberrypi4 #raspberrypico #rapi #rapi4 #embedded #rtos #rtthread #rt-thread #realtime