Arduino nano + microSD module + ethernet module does not assign IP address
As already written in the question I opened the problem was solved by performing this change to the card reader: https://forum.arduino.cc/index.php?topic=360718.msg2942160#msg2942160

Micro SD readers equipped with LVC125A chips have the MISO output perpetually enabled and disrupting communication with other devices.

I thank one last time @Juraj for his support: without his advice I could never have solved my problem.
Thank you!