Beta 5.900 from 09.09.2021 crashes (split screen)

After the update from 09.09.2021 (Beta 5.900) the app does not start anymore !
The problem is the activated split screen which crashes the app.
Without split screen the app is properly running.

We use the issue tracker on GitHub for bug reports. This one is tracked as #5665.

The fix will be included in K-9 Mail 5.901.