There's OpenAirScan for iPhone/iPad now, which was created somewhat recently, in 2023.

https://apps.apple.com/us/app/openairscan/id1663611384

It doesn't have 100% compatibility with driverless scanning, but it's trying. If you share your scanner using AirSane on the Raspberry, it may work.

Strange that iOS doesn't have native scanning capabilities, only printing via AirPrint.