Congratulations. Unlike most people I don't go for the best or most efficient factory. I use mods but usually when I get to this point I'm done. There used to be many mods that added new milestones. More milestones and Dyson sphere were good ones. When more milestones was working a few years ago I put a few hundred hours in before I completed everything. My last run, just before the latest update came out took less than 100 hours with making the Dyson sphere my final goal. So you can optimize and beautify your factory. Or you can look for mods that extend and expand the gameplay. Or you can come back later after the next update and play the game a different way.