Thank you for your Reply.
I've also had enough due to these 2 stupid Packages and decided to just mirror the entire pve-no-subscription and pbs-no-subscription Repositories.
I am using a heavily patched Version of debmirror (Perl ... sigh...
If the Router doesn't understand VLANs, then Router's traffic will default on the default untagged VLAN (Default ID: 1).
You can configure the untagged VID in Proxmox for the NIC, or add another Virtual NIC and set that as untagged instead.
Ever since Proxmox VE started requesting / recommending the installation of proxmox-offline-mirror-docs / proxmox-offline-mirror-helper (either as Dependency or as recommended Packages), I had all Clients failing to download these Packages via...