Any advice, please, how to recover it to any functional state?
In response to your help question, the original backup was for testing purposes only.

...but it wants to type the key on device so no chance to go further...
The latest generation of GPS Mio is encoded between the device and the software.

Any advice how to unlock/fix Navman?
If you do not have a copy of this device, as far as I know, there is no way to restore GPS to its normal state.

If you want the GPS Mio 5400LM to work, use the unlock I left in post 2, you can change the interface buttons, among other things.
You can try some navigation software available here in the forum and always have the most current maps, such as radars and other services.