My serial between raspberry and arduino works at 9600 baud
That is the baud rate that your sketch uses. It has absolutely nothing to do with the baud rate of the upload. That is determined by the bootloader.
and with verbose mode it says “Overriding Baud Rate : 115200”
If you are using an official Arduino Nano board bought since 2018, that is the correct baud rate.
If you are using an older official Arduino Nano, then the correct baud rate is 57600 and you should use the FQBN for the “ATmega328P (Old Bootloader)” version of the Nano board definition:
arduino-cli upload --verbose -p /dev/ttyAMA0 --fqbn arduino:avr:nano:cpu=atmega328old aquaponie-full-time
Is it possible to specifie the baud rate to arduino-cli ?
As I showed you above, the Arduino Nano board definition has custom options for the two different bootloader versions that were used by the board. It would be absolutely pointless to offer the ability for the user to specify arbitrary upload baud rates because the bootloader uses one specific baud rate. If you use any other baud rate, the upload would simply fail.
But all of this is just a distraction. Your problem is that you are not able to reset the board. If you manage to fix that problem and are still unable to upload then we can do further troubleshooting, but for now it’s pointless.