Hi joby81,
Thanks for posting in Apple Support Communities.
we understand that after updating that the projector is unable to work with your iPhone. It is up to third-parties to make their software compatible with available devices. It would be best to check with the manufacturer of the projector for compatibility and if there is an update needed to make the projector compatible.
We're not clear on how you're connecting the projector, but if you're doing so by Bluetooth, there are a few steps that can be performed.
To get help pairing a Bluetooth accessory—like a wireless keyboard—to your iOS or iPadOS device, try these steps:
1. Make sure that your Bluetooth accessory and iOS or iPadOS device are close to each other.
2. Turn your Bluetooth accessory off and back on again.
3. Make sure that your Bluetooth accessory is on and fully charged or connected to power. If your accessory uses batteries, see if they need to be replaced.
4. If there's an app that you use with the Bluetooth accessory, go to Settings > Privacy > Bluetooth on your iOS or iPadOS device, and make sure that you've turned on Bluetooth for the app.
Find these and additional steps in If you can't connect a Bluetooth accessory to your iPhone, iPad, or iPod touch.
Regards.