[2023] 0 pops showing up in the Demographics tab

By disabling your mods and redownloading, it sounds like you've covered most of the troubleshooting bases. I'd head to support.paradoxplaza.com and open a ticket. Customer Support will be able to help you with this issue!

So! We checked in-game, and this is an issue for us as well -- would you be so kind as to submit a bug report so we can have the team look into it?

https://forum.paradoxplaza.com/forum/forums/stellaris-bug-reports.941/

Thanks!