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The following is a quote from page 59 of the Atmel ATmega328P manual.
“If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).”
If this is true for the Controllino also, the output pin should not float if a zero is written to the pin. Of course, the usual error is with the programmer, so maybe I am missing a configuration step.