I have code written 20+ y/o, which is still running in production at multiple places in the world. It's for non-trivial soft-realtime embedded system processing

I have code written 20+ y/o, which is still running in production at multiple places in the world. It's for non-trivial soft-realtime embedded system processing PBs of data in realtime, not some CRUD app which can be easily spit out by GitHub Copilot or ChatGPT. But yes, every SW/HW/systems project should come with an expiration date. From quick-and-dirty or throwaway, to extended longevity/support. It's important to choose the tech stack, architecture, and SDLC accordingly. e.g. don't use ecosystem with accelerated bit rot like nodejs/npm for long-term projects. Similarly don't use C++, Rust, etc. for one-off scripts or prototypes. Same for Agile/Scrum vs upfront design/RUP/mini-waterfall.