onBackPressed() deprecated, What is the alternative?

According your API level register:

• onBackInvokedDispatcher.registerOnBackInvokedCallback for API level 33+
• onBackPressedDispatcher callback for backword compatibility “API level 13+”

This requires to at least use appcompat:1.6.0-alpha03; the current is 1.6.0-alpha04:

 implementation 'androidx.appcompat:appcompat:1.6.0-alpha04'

// kotlin
import androidx.activity.addCallback

if (BuildCompat.isAtLeastT()) {
    onBackInvokedDispatcher.registerOnBackInvokedCallback(
        OnBackInvokedDispatcher.PRIORITY_DEFAULT
    ) {
        // Back is pressed... Finishing the activity
        finish()
    }
} else {
    onBackPressedDispatcher.addCallback(this /* lifecycle owner */, object : OnBackPressedCallback(true) {
        override fun handleOnBackPressed() {
            // Back is pressed... Finishing the activity
            finish()
        }
    })
}

// ====================================================
/* Or for lambda simplicity: */
// ====================================================
if (BuildCompat.isAtLeastT()) {
    onBackInvokedDispatcher.registerOnBackInvokedCallback(
        OnBackInvokedDispatcher.PRIORITY_DEFAULT
    ) {
        // Back is pressed... Finishing the activity
        finish()
    }
} else {
    onBackPressedDispatcher.addCallback(this /* lifecycle owner */) {
        // Back is pressed... Finishing the activity
        finish()
    }
}

UPDATE:

Thanks to @ianhanniballake comment; you can just use OnBackPressedDispatcher even in API level 33+

The OnBackPressedDispatcher is already going to be using the Android T specific API internally when using Activity 1.6+,

So, you can just do:

// kotlin
import androidx.activity.addCallback

onBackPressedDispatcher.addCallback(this /* lifecycle owner */, object : OnBackPressedCallback(true) {
    override fun handleOnBackPressed() {
        // Back is pressed... Finishing the activity
        finish()
    }
})

// ====================================================
/* Or for lambda simplicity: */
// ====================================================
onBackPressedDispatcher.addCallback(this /* lifecycle owner */) {
    // Back is pressed... Finishing the activity
    finish()
}

// java
import androidx.activity.OnBackPressedCallback;

getOnBackPressedDispatcher().addCallback(this, new OnBackPressedCallback(true) {
    @Override
    public void handleOnBackPressed() {
        // Back is pressed... Finishing the activity
        finish();
    }
});

Note that you shouldn’t override the onBackPressed() as that will make the onBackPressedDispatcher callback not to fire; check this answer for clarifying that.