This is absolutely a thing. I also have a side project like that, a library that I can come back to after working 9 hours a day on some trash garbage codebase

This is absolutely a thing. I also have a side project like that, a library that I can come back to after working 9 hours a day on some trash garbage codebase that unironically makes me want to commit die. It helps to know that there's a program or several, no matter how small, that are actually well thought out and carefully implemented.