For all my Proxmox LXC/VMs I always try to set a static IP so I can remember services more easily, each time I have to reach out to the AI of the month to ask the same questions, so I'm going to make it simple for myself...
Edit interfaces file: /etc/networks/interfaces.
iface ens18 inet static
address 10.0.1.100
subnet 255.255.255.0
gateway 10.0.1.1
dns-servers 10.0.1.1
For some reason, no matter the DNS servers I use, it doesn't resolve a domain name, only an IP address, so I have to also edit /etc/resolv.conf
nameserver 10.0.1.1
nameserver 1.1.1.1
At the end I either restart networking or reboot the VM/LXC
systemctl restart networking