UserDefaults works fine for me. Note that the suitName must be the same as your app group id.
ejeklint
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Problem solved! Rather intricate, but a test application using a DriverKit USB HID extension and installed with System Integrity Protection turned off, started to crash in 10.15.7. Solution was to turn off SIP and delete the rogue extension. The extension should automatically be deleted when the owning app is deleted, but that didn’t work, apparently.
DUH! Problem was elsewhere (wrong settings in multimeter), just a coincidence it happened when upgrading to Big Sur. 🤦🏼♂️