The path to the assets for devices with Android < 10 has changed (since the nb187 release) from:
/storage/emulated/0/AppInventor/assets/
to:
/storage/emulated/0/Android/data/edu.mit.appinventor.aicompanion3/files/AppInventor/assets/
Therefore, the extension no longer worked under Android <10 with Companion.
Here is the update that fixes this problem:
MyFonts.aix (5.8 KB)