I have very good news.
While analyzing the chipset of the network card, I realized that it was an Intel (and not a realtek) I219-LM and that it was an old chipset.
So I downloaded the bzImage 5.15.98 kernel and made it available in the appropriate folder on the FOG server, calling it bzImage_5.15.98.
Then, in the host description, I put bzImage_5.15.98 in front of the machine kernel.
And oh magic, everything went back to the way it was before 13 GB/mn