Simplest network for VM ?

[ybabel]

Hello, I'm new to proxmox (6). I previously used Virtual Box and vSphere.
I installed proxmox on a Kimsuffi server. It's working well. I can install a VM (a Ubuntu server 18.04 LTS), but I cannot get the network to work. I have tried various tutorial but I'm not used to configure networks on linux and I cannot figure out what's wrong. Many tutorials refers to PVE5, or specific configurations.

By default my /etc/network/interface is :

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

iface enp1s0 inet manual

auto vmbr0
iface vmbr0 inet dhcp
  bridge-ports enp1s0
  bridge-stp off
  bridge-fd 0

On VirtualBox I just add a bridge and that's all ... my VM can access internet. Here, it does not work the same.
What should I do ?
AFAICT I have 2 solutions : fix IP or DHCP.
I have tryed fix IP with this host configuration :

auto lo
iface lo inet loopback

auto enp1s0
iface enp1s0 inet static
        address  188.xx.xx.41
        netmask  255.255.255.0
        gateway  188.xx.xx.254

auto vmbr0
iface vmbr0 inet static
        address  10.10.10.1
        netmask  255.255.255.0
        bridge_ports none
        bridge_stp off
        bridge_fd 0
        post-up echo 1 > /proc/sys/net/ipv4/ip_forward
        post-up iptables -t nat -A POSTROUTING -s '10.10.10.0/24' -o enp1s0 -j MASQUERADE
        post-down iptables -t nat -D POSTROUTING -s '10.10.10.0/24' -o enp1s0 -j MASQUERADE

and then on the VM 50-cloud-init.yaml

network:
  version: 2
  ethernets:
    ens18:
      dhcp4: no
      addresses: 
        - 10.10.10.2/24
      gateway4: 188.xx.xx.254
      nameservers:
        adresses: [8.8.8.8]

Ideally I would like to have a DNS so that I can install new VM as needed but for now, static IP working would just be fine because after 2 days of trying, I'm confused and tired.

 

[ybabel]

I have also tryed "10.10.10.1/24" for the IP host.