All my other devices uses the screen mirroring function without any issues.
Is this something new with this Roku model?
Screen mirroring on Roku devices=Miracast (Settings/System/Screen mirroring) - you would need to install a Miracast-compatible app to use Roku's screen mirroring for your Apple devices.
Apple devices support AirPlay2 for for mirroring/casting, which Roku recently added support for (Settings/Apple AirPlay and HomeKit).
If you dont see Settings/Apple AirPlay and HomeKit then your Roku device doesnt have AP support (and you wont be able to use AirPlay-mirroring or AirPlay-casting).
If your device does have AirPlay support but you still have issues, then:
1) Verify you have the latest AirPlay support: A) Using remote: Home 3x, Up 2x, L, R, L, R, L (AirPlay should be 1.1.14-104 or later) B) Settings/System/System update/Check now (should be 10.0.0-4195 or later for most models) - try again
2) Disable & Re-enable WiFi on the Apple devices - try again
3) Restart all devices (Rokus, Apples, router/modem) - try again
4) Reset the paired devices: Settings/Apple Airplay and HomeKit/Require Code/Reset Paired Devices - try again
5) Setup HomeKit: Settings/Apple Airplay and HomeKit/Setup HomeKit - try again
6) Switch either Rokus or Apples from 5Ghz to 2.4Ghz, or from 2.4Ghz to 5Ghz - try again
7) Switch Roku's display output to 1080p - try again