I’ll have to disagree with this. Adding new features is a problem if old things break but otherwise it just makes future programs easier to write.
You should be writing your next set of code with the newest features if they cut down dev time, cut down bugs or make that area more maintainable
Coming back to code after a year is hard regardless of language. I’ve had C code I came back to after a year that was dead simple language feature wise but hard as hell to follow business wise. I would actually argue more modern features like Union types in typescript has actually made it easier for me. “Oh this function has to handle two cases of objects an object with an id and without an id”