## have similar situation:
install `pve6.3` on pure `debian 10.8`
```
$ cat /etc/debian_version
10.8
$ apt list proxmox-ve
Listing... Done
proxmox-ve/stable,now 6.3-1 all [installed]
$ apt list ifupdown ifupdown2
Listing... Done
ifupdown2/stable,now 3.0.0-1+pve3 all [installed]...