Start with writing a custom cpu emulator -> machine code -> assembler -> compiler

Sounds hard but it's quite easy with stack architecture :) Easier than learning JS for sure

nowadays it is somewhat easier to make your own programming language, than it was 10 to 20 or 30 years ago, because there are a lot of resources such as tutorials and open source projects available on the internet, in both text and video formats, to learn from. there are also many online forums where you can ask questions and get answers and advice.