Guidance or links for cross compiling toolchain for microcontrollers

You say there is loads of documentation out there but for some reason i can't find it. My current search efforts are all clogged up with platformio, arduinocmake project, or just basic arduino studio tutorials. I stated as much in my original post - "There isn't any tutorials or documentation that I can find".

If you have any resources that you can point me to other than 'just google it' that would be helpful.