Proxmox Helper scripts: DNS problem?

[mago]

Hi folks,
I am quite new to Proxmox and setting up my first LXC using the Proxmox helper scripts is driving me nuts.
Just using one of the scripts (e.g. iobroker, grafana, pihole, ...) always brings me to the famous(?) error:

[ERROR] in line 23: exit code 0: while executing command "$@" > /dev/null 2>&1
The silent function has suppressed the error, run the script with verbose mode enabled, which will provide more detailed output.

Following the advice and calling the script in advanced mode with more verbosity shows up a DNS problem:

    ____  ____   __  ______  __    ______
   / __ \/  _/  / / / / __ \/ /   / ____/
  / /_/ // /___/ /_/ / / / / /   / __/   
 / ____// /___/ __  / /_/ / /___/ /___   
/_/   /___/  /_/ /_/\____/_____/_____/   
 
Using Advanced Settings
Using Distribution: debian
Using debian Version: 12
Using Container Type: 1
Using Root Password: Automatic Login
Container ID: 100
Using Hostname: pihole
Using Disk Size: 2
Allocated Cores: 1
Allocated RAM: 512
Using Bridge: vmbr0
Using IP Address: dhcp
Using Gateway IP Address: Default
Using APT-Cacher IP Address: Default
Disable IPv6: no
Using Interface MTU Size: Default
Using DNS Search Domain: Host
Using DNS Server IP Address: Host
Using Vlan: Default
Enable Root SSH Access: no
Enable Verbose Mode: yes
Creating a Pihole LXC using the above advanced settings
 ✓ Using local for Template Storage.
 ✓ Using local-lvm for Container Storage.
 ✓ Updated LXC Template List
 ✓ LXC Container 100 was successfully created.
 ✓ Started LXC Container
 ✓ Set up Container OS
 ✓ Network Connected: 192.168.178.85 2003:c0:5706:d400:be24:11ff:fe42:7378
 ✓ IPv4 Internet Connected
 ✗ IPv6 Internet Not Connected
 ✗ DNS Lookup Failure
Ign:1 http://security.debian.org bookworm-security InRelease         
Ign:2 http://deb.debian.org/debian bookworm InRelease               
Ign:3 http://deb.debian.org/debian bookworm-updates InRelease
Ign:2 http://deb.debian.org/debian bookworm InRelease               
Ign:1 http://security.debian.org bookworm-security InRelease         
Ign:1 http://security.debian.org bookworm-security InRelease         
Ign:3 http://deb.debian.org/debian bookworm-updates InRelease       
Ign:2 http://deb.debian.org/debian bookworm InRelease               
Err:1 http://security.debian.org bookworm-security InRelease         
  Temporary failure resolving 'security.debian.org'
Ign:3 http://deb.debian.org/debian bookworm-updates InRelease
Err:2 http://deb.debian.org/debian bookworm InRelease
  Temporary failure resolving 'deb.debian.org'
Err:3 http://deb.debian.org/debian bookworm-updates InRelease
  Temporary failure resolving 'deb.debian.org'
Reading package lists... Done   
W: Failed to fetch http://deb.debian.org/debian/dists/bookworm/InRelease  Temporary failure resolving 'deb.debian.org'
W: Failed to fetch http://deb.debian.org/debian/dists/bookworm-updates/InRelease  Temporary failure resolving 'deb.debian.org'
W: Failed to fetch http://security.debian.org/dists/bookworm-security/InRelease  Temporary failure resolving 'security.debian.org'
W: Some index files failed to download. They have been ignored, or old ones used instead.
Reading package lists... Done
Building dependency tree... Done
Calculating upgrade... Done
 /0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
 ✓ Updated Container OS
Reading package lists... Done
Building dependency tree... Done
 -The following additional packages will be installed:
  libcurl4
The following NEW packages will be installed:
  curl libcurl4
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 704 kB of archives.
After this operation, 1,359 kB of additional disk space will be used.
Ign:1 http://deb.debian.org/debian bookworm/main amd64 libcurl4 amd64 7.88.1-10+deb12u7
Ign:2 http://deb.debian.org/debian bookworm/main amd64 curl amd64 7.88.1-10+deb12u7
Ign:1 http://deb.debian.org/debian bookworm/main amd64 libcurl4 amd64 7.88.1-10+deb12u7
Ign:2 http://deb.debian.org/debian bookworm/main amd64 curl amd64 7.88.1-10+deb12u7
Ign:1 http://deb.debian.org/debian bookworm/main amd64 libcurl4 amd64 7.88.1-10+deb12u7
Ign:2 http://deb.debian.org/debian bookworm/main amd64 curl amd64 7.88.1-10+deb12u7
Err:1 http://deb.debian.org/debian bookworm/main amd64 libcurl4 amd64 7.88.1-10+deb12u7
  Temporary failure resolving 'deb.debian.org'
Err:2 http://deb.debian.org/debian bookworm/main amd64 curl amd64 7.88.1-10+deb12u7
  Temporary failure resolving 'deb.debian.org'
E: Failed to fetch http://deb.debian.org/debian/pool/main/c/curl/libcurl4_7.88.1-10%2bdeb12u7_amd64.deb  Temporary failure resolving 'deb.debian.org'
E: Failed to fetch http://deb.debian.org/debian/pool/main/c/curl/curl_7.88.1-10%2bdeb12u7_amd64.deb  Temporary failure resolving 'deb.debian.org'
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

[ERROR] in line 17: exit code 0: while executing command $STD apt-get install -y curl

I checked DNS resolution on host level:

root@proxmox:~# nslookup www.heise.de
Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
Name:   www.heise.de
Address: 193.99.144.85
Name:   www.heise.de
Address: 2a02:2e0:3fe:1001:7777:772e:2:85

- I tried to set my local DNS Gateway as DNS in Proxmox settings, as well as some external servers like in the example
- I tried to disable IPv6 in helper script setup as well as at my local router (FritzBox)
- I re-installed the LXCs many times and also rebooted Proxmox

None of those actions changed anything in the behavior, and meantime I'm running out of ideas. I found some hints on the web about this or similar problems, some of them mentioned above, none of them helped or was applicable.

Does anyone have an idea?

Thanks in advance!

Cheers