Edit: SOLVED. It turns out, I had uninstalled the system package com.android.inputdevices , which is used to locate available keyboard layouts.

7qPJAQyGqVGqZM9.png

dUwL1oofLuH68a1.png

This is on a Samsung Galaxy S23 using Heliboard and Simeji as software keyboards. Samsung’s keyboard is uninstalled. On my Galaxy Tab A9+ with the exact same configuration, I am able to set the default keyboard layout…

Any ideas?