After enabling readback protection, the device will have limited debug capabilities. To restore full debug access, you need to recover the device, which erases all flash memory contents.
To recover a device with protection enabled, use the recover command:
nrfutil device recover --serial-number <serial_number>
For multi-core devices like nRF53 Series, make sure to recover the network core before the application core:
nrfutil device recover --core Network --serial-number <serial_number>
nrfutil device recover --core Application --serial-number <serial_number>
See Recovering the device for more detailed information about the recovery process for different device families.