App always launches at main activity from launcher despite alwaysRetainTaskState in singleTask mode

Question

I have a launcher Activity declared like so:

<activity
            android:name=".MainActivity"
            android:exported="true"
            android:alwaysRetainTaskState="true"
            android:launchMode="singleTask"
            android:windowSoftInputMode="adjustResize"
            android:theme="@style/Theme.MyApplication.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

In this activity I have a Fragment and inside the fragment in response to a user action I launch another Activity like so:

(this.context as? Activity)?.let { ctx ->
   ctx.startActivity(Intent(ctx, SomeOtherActivity::class.java))
}

The second activity is also declared as singleTask like so:

<activity
            android:name=".ui.SomeOtherActivity"
            android:exported="false"
            android:launchMode="singleTask"
            android:windowSoftInputMode="adjustResize" />

This adds the new activity correctly to the back stack so the user can use back OS button to go back to MainActivity no problem.

Now if I open SomeOtherActivity, go to home screen and launch my app again, I see MainActivity instead.

According to some other answers, setting android:alwaysRetainTaskState should be a solution but that didn't work.

How can I get the app to show the last activity user was on without manually having to store that in the Shared Preferences?

For me the flow involves quite a few activities in a liner fashion (e.g. user picks something from one list, goes to that activity which shows another list, the selection there is another activity and so on..)

If I remove android:launchMode="singleTask" from both activities then I do end up going back to SomeOtherActivity.

However, the way my application is designed once user selects something in the first activity the context for underlying singleton classes switches so I want to only ever have one instance of ALL my activities to avoid the UI thinking the user chose A when the underlying singleton and data persistence thinks it's B (because that somehow came in another instance of activity).