Ive always just used C. From my recollection, there’s an avr libc library. There’s tutorials online for how to do it. The big thing is once you have that progression path with knowledge like that book I linked, you have a lot of freedom.
Some chips can use Micro Python or even Rust. I have not explored those myself.
How hard is to change the programming language? I think in the video they use the Arduino programming IDE.