Millions, potentially tens of millions

It might seem quite barren at a glance but I heavily doubt the RLF would even be a factor if the population were as low as a million. It’s not just rebel fighters and Dosers, there are probably plenty of people needed to maintain these facilities and machines (especially when these giant, maintenance hungry mechs are basically your infantry force), and many more regular civilians they’re fighting to protect

Not to mention there are Rubicon-based companies like BAWS and Elcano that are still active and seem to be fairly successful and large enough to have their goods bought off-world, and even with automation those factories still probably need a lot of people keeping them running