So it seems the Requires System Keyboard part doesn’t work unless you add a ‘ManifestRequirementsOverride.txt’ to your projects Build\Android folder. Also, you may need to delete the content of Intermediate\Android for your project.
The ‘ManifestRequirementsOverride.txt’ file should contain the following:
<uses-feature android:name="oculus.software.overlay_keyboard" android:required="false"/>
The keyboard then shows up; maybe Epic will fix the button in ‘Project Settings/Android’
in a few years, but for now, here’s another workaround.