Homekit - can't connect any device with iOS 16.3., but on different iPhone with iOS 16.0.3 I can

Hey there rushqone,

Thanks for reaching out to the Apple Support Communities.

To get started, we noticed you stated that the issue was occurring on your iPhone running iOS 16.3, was that correct? If so, it does look like an iOS update would be available for your iPhone to iOS 16.3.1. Since updating can often bring the latest features, security updates, and bug fixes, try updating the iOS and test the issue again.

Update your iPhone or iPad - Apple Support

Update your iPhone or iPad wirelessly

1. Back up your device using iCloud or your computer.

2. Plug your device into power and connect to the internet with Wi-Fi.

3. Go to Settings > General, then tap Software Update.

4. If you see more than one software update option available, choose the one that you want to install.

5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.

You'll also want to ensure that you're signed into the same iCloud account on all devices as well. For more details on troubleshooting issues with connecting an accessory to the Home app, check out this link here: Add an accessory to the Home app - Apple Support

If you can't add an accessory

* Update your iPhone or iPad to the latest version of iOS or iPadOS.

* Make sure that your accessories support HomeKit, AirPlay, or Matter.

* To use and manage your home in the Home app on all of your devices, sign in to iCloud with your Apple ID on every device. Then turn on iCloud Keychain and Home in iCloud Settings.

If the issue remains after going through the steps above, the next best option would be to reach out to Apple Support directly from this link here: Contact - Official Apple Support

We hope that's able to help.

Best regards.