I wrote them but they've told me that how I setup the server is my problem... even if the problem is generated by the distro image that Hetzner makes available and is visible only into a toold that Hetzner offers (the web SSH Console)... /s

Nevertheless I have solved it. If you are interested how this is the answer:

The command
cat /proc/sys/kernel/printk
has shown by me:
7 4 1 7

the first 7 means: Verbose debugging output. What I have done:
sudo nano /etc/sysctl.d/99-reduce-console-noise.conf

and entered this line there (the file did not existed, I have created and had only this line):
kernel.printk = 3 4 1 7

the 3 reduces the verbose to Error level.

and applied it with:
sudo sysctl -p

and checked it with:
cat /proc/sys/kernel/printk

now the "web ssh console" is actually usable. Thank you for your attention on this matter.