Dedicated Server Can't reboot Debian 10 server after installing KVM bridge

Hello all,
so I installed kvm qemu on my server and tried to install a bridge. After rebooting the server does not raise the network anymore. I then via rescue deleted the file /etc/network/interfaces which is the stat it was before, i.e. no interfaces file but it will still not come up.

In syslog there are lots of messages type "network unreachable resolving '_.debian.pool.ntp.org/A/IN': 2001:500:1::53#53"

and error

error resolving pool 3.debian.pool.ntp.org: Temporary failure in name resolution (-3)

Unfortunately my pre-crash backup does not have the correct owners and groups but I can check on files etc. Can someone point me in the right direction?
Thanks, answers in French, Spanish or German also ok.