I tried your suggestions, and it worked. The game could load the lots again, so the issue seems to have been in my Sims 4 folder somewhere.
I spent even more time going through the EA forums and saw some people suggesting that there were problems with the ts4script-files. So, I tried to add mods that don't use ts4script-files, and the game continued to work. Eventually, I renamed the folders again (so the game would use my old folder), and using only mods without ts4script-files, the game seemed to work again. Which makes no sense since I removed ALL mods and CC before even trying that...?
The only thing I could find in my old folder that was a bit off was that some mods had created files in other folders (I think there was something in the Tray folder, possibly elsewhere, but I don't remember exactly). I didn't think to remove those the first time I removed all mods, so I don't know if that might have caused some issues. That's the only thing that I can think of that was different between the old and new folders (besides the obvious stuff like saves, etc.).
This patch has genuinely caused more issues than many full updates🙃
Thanks for the help, though!