HomeKit broken after iOS18 update

Since updating my AppleTV's, HomePods (and minis) and iOS devices to iOS18, I get an error saying none of my hubs will connect, and thus HomeKit is essentially dead and useless. I've tried removing the hubs and re-adding them, but now I get errors on my iPhone or iPad saying the devices couldn't be setup.

I went so far as to setup a separate network with a different router and started a new home, and trying to add a factory reset HomePod mini, and I'm getting a failed setup error. I genuinely don't know what else to try, as this pretty much checks off all of Apple's support issues. (Restarting iPhones/iPads used for setup, rebooting routers, starting from scratch, etc etc...)

Any other suggestions out there?