iOS16 Homekit will no longer add new accessories on 2.4GHz wifi

Hello tgwaste, 

Welcome to the Apple Support Communities. 

We understand your situation and how you have been unable to add some accessories in the Home app. We’d be happy help you with this so that you can start using these HomeKit compatible accessories with your Apple devices. 

From what you have described, we understand that the issue may be caused by a network problem. To start, we would suggest implementing these suggestions for the most reliable Wi-Fi connection. This may involve changing some of your existing router settings: Recommended settings for Wi-Fi routers and access points - Apple Support

We would also suggest following this Apple Support article when adding a new accessory to your home: Add an accessory to the Home app - Apple Support

Some additional troubleshooting to try would be to: 

1. Install any updates available for your Apple devices. 
2. Make sure that your accessories support HomeKit, AirPlay 2, or Matter.
3. Confirm that the same Apple ID is being used with every Apple device, and that iCloud Keychain and Home are enabled in the iCloud settings for your devices. 

If you continue to notice a problem when adding new accessories, please contact Apple Support directly for more help. 

We hope that this information helps you find a solution. 

Have a great day!

I'm having the same issue, using an Eero Mesh network setup. Have you figured out any way to add new accessories? All my existing HomeKit devices work just fine, but I can't add any new devices since updating to iOS 16. Very frustrating.

Okay, so I have an old iPad mini using iOS 15, and I was able to add devices to HomeKit using that. So, it's definitely some sort of bug. I'm not sure if it's with my Eero network, or with iOS 16.