Mcu 'mcu': Unable to open serial port: [Errno 2] could not open port /dev/serial/by-id/

This is quite surely not needed for this board.

Please refer to Manta-M8P/V2.0 at master · bigtreetech/Manta-M8P · GitHub and in particular Manta-M8P/V2.0/Firmware/generic-bigtreetech-manta-m8p-V2_0.cfg at master · bigtreetech/Manta-M8P · GitHub for the correct setting.

This is exactly what this linked knowledge-base article Issues flashing the printer board is about: There is only one truth when managing firmwares and settings. There is absolutely no “well, lets use this weird setting”