After a bumpy research and some failed attempts, the old Raspberry could be reawakened with the RAK 831 in the V3 TTN.
Here is the link to the solution:
- Last RaspiOS Lite on SD
- Reboot and update (of course set the WiFi and network data up to date in advance)
- Install from Git
- Software loaded via Git, installed and then configured
- The gateway setting about the available Global_Konfig (in the TTN to the GW available) entered
Thanks to the community