FYI, on Roku devices screen mirroring (Miracast=Settings/System/Screen mirroring) and AirPlay (Settings/Apple AirPlay and HomeKit) are two different protocols/functionality.
You'd need to test the AirPlay with an Apple device (barring using third party apps that allow Miracast), and the Miracast with an Android/Windows device (barring using third party apps that allow AirPlay).
1) Verify you have the latest AirPlay support:
A) Settings/Apple AirPlay and HomeKit/About AirPlay/AirPlay version=220.127.116.11
B) Settings/System/System update/Check now (RokuOS should be 10.0.0-4209 or later) - try again
2) Verify your devices arent connected to a Guest SSID or otherwise have AP/Client Isolation enabled on the SSID - try again
3) Verify Roku AirPlay with phone HotSpot - enable HotSpot (2.4Ghz), connect/tether Roku to Hotspot - try again
4) Disable & re-enable WiFi on the Apple devices - try again
5) Restart all devices (Rokus, Apples, modem/router/gateway) - try again
6) Disable AirPlay: Settings/Apple AirPlay and HomeKit/AirPlay=off, Restart Roku, Enable AirPlay - try again
7) Reset the paired devices: Settings/Apple AirPlay and HomeKit/Require Code/Reset Paired Devices - try again
😎 Setup HomeKit: Settings/Apple Airplay and HomeKit/Setup HomeKit - try again
9) Switch either Rokus or Apples from 5Ghz to 2.4Ghz, or from 2.4Ghz to 5Ghz - try again
10) Set display to 1080p: Settings/Display type/1080p TV - try again
11) Network connection reset: Settings/System/Advanced system settings/Network connection reset - try again
12) Factory reset: Settings/System/Advanced system settings/Factory reset <--- Last resort