Problems with board_build.mcu = atmega328pb

That option doesn’t (usually) do anything! It is supposed to force the avrdude utility to do the upload when the signatures don’t match with the supplied microcontroller name.

I notice from the firmare.hex full path listed, that you are on Windows. Have you installed a driver for the Atmel Ice programmer on that test system? Have a look in the drivers section when the device is connected, there might be a “warning triangle” against the COM/USB port – sorry, I’m not a Windows user or guru – which would indicate a problem. It’s usually a driver that’s missing.

I also don’t have an ATmega328pb, unless the chip on my Nano clone is one, but my eyes are too ald to see the tiny writing! :cry: