Don't enable Wi-Fi calling on the Dumber Mini (yet)

The DumberOS September update added a Wi-Fi calling toggle. Don't turn it on. After the reboot the SIM PIN is accepted, but there is no service and the SIMs menu is greyed out.

Check if you're affected

adb shell getprop sys.phh.stock_mtk_ims
adb logcat -d -b crash | grep MtkIsimUiccRecords

If the first prints true and the second shows com.android.phone crashing with an IllegalAccessError in MtkIsimUiccRecords, that's it. The phone process crashes every few seconds once the SIM is unlocked.

Fix

The toggle only creates a flag file. Delete it and reboot. This needs root, so first enable Settings > System > Developer options > Rooted debugging.

adb root
adb shell rm /metadata/phh/dumber_mini_stock_ims
adb reboot

After the reboot sys.phh.stock_mtk_ims is false and the SIM works again. Turn rooted debugging off afterwards.