I don’t know either, but I’d like to have some NV memory in a XIAO and I found No EEPROM or NVR in XIAO? which suggests that FLASH memory is available, survives power down, but not new code upload. I’ve been using “setup” to hold permanent data but when I need that configuration data to change then I’m hoping I can write to flash. I haven’t yet followed the links in that thread…