Linux header 4.9.0-11-amd64 is missing in debian
Solution 1:
Debian 9 (stretch)?
from this thread's answer
edit (or create) /etc/apt/sources.list.d/snapshot.list
deb http://snapshot.debian.org/archive/debian/20190925T034604Z stretch main
deb http://snapshot.debian.org/archive/debian/20190925T034604Z stretch-updates main
deb http://snapshot.debian.org/archive/debian-security/20191020T221221Z stretch/updates main
note : the 20190925T034604Z is from this answer date : sept 25 '19
then:
apt -o Acquire::Check-Valid-Until=false update
apt install linux-headers-4.9.0-11-amd64
Or you can just install newer kernel