/etc/pve/local/pve-ssl.key: failed to load local private key (key_file or key) at /usr/share/perl5/

Same problem as described here:
https://forum.proxmox.com/threads/problem-with-installing-proxmox-ve-on-debian.44316/

But my /etc/hosts seems fine:

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root@debian:/etc/apt/trusted.gpg.d# cat /etc/hosts
127.0.0.1 localhost
127.0.1.1 debian
192.168.1.3 proxmox pvelocalhost

following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters...

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