dhclient eth0
apt update
apt install network-manager-gnome

Or, if you don't want a gui program for connecting to the network, you could just edit /etc/network/interfaces and add the following:

auto eth0
iface eth0 inet dhcp

You can do one or the other, but don't do both of those things.

how to try to recover it pls.

I did start from USB stick where chimaera without other files is present

update

upgrade

snapshotped

(snapshot did refuse to build ISO)

I did copy /home/work/ content into a free partition

update grub

an restart

Chimaera did start willing and all seem to work ...
... excepted the automatic connection with the wired internet modem.

Principal question:

What can I try to do?

Accessory question:

Can I, as soon I get internet again, update that new actual installation chimaera and upgrade it to the actual daedalus? Is perhaps a special way known or what can I try to do?