I am using expo-audio library to create a simple alarm app. The requirement is to use built-in speaker always, regardless if the Bluetooth headphones are connected.

I can see in the docs https://docs.expo.dev/versions/latest/sdk/audio/#audiomode

that audiomode accepts shouldRouteThroughEarpiece property but only for Andriod.

Can this feature be exposed on iOS as well to force playback using the device's speakers?

It should be relatively straightforward to implement, and should help will all alarm related user experiences.