I find the games kinda polar opposites in terms of interest- Rimworld was great for a certain amount of time then I basically lost interest. I still go back to it from time to time, build a new colony and let it run its course. Conversely I've been running Factorio on a headless server for 4+ years now. There's always something to fix or improve, it never ends or (for me) gets boring. I've recently upgraded to Space Age and am refactoring everything for the new rules, which is probably going to take another four years!
Pre Space-Age, vast swathes of my factory were dedicated to producing Satellites. Now they're no longer required, merely deconstructing all that infrastructure took my 20,000 bots about 12 hours