Find the interface code

ip link show | grep "^[0-9]:" | awk '{print $2}' | sed 's/:$//'

Set up netplan with persistent VLAN configuration

INTERFACE="enp6s0"
SWITCH=4000
NUMBER=12

sudo bash -c "umask 0077; cat > /etc/netplan/99-vlan.yaml << 'EOF'
network:
  version: 2
  renderer: networkd
  ethernets:
    $INTERFACE:
      dhcp4: false
  vlans:
    $INTERFACE.$SWITCH:
      id: $SWITCH
      link: $INTERFACE
      mtu: 1400
      addresses:
        - 192.168.100.$NUMBER/24
EOF
"

sudo netplan apply

Dedicated-Cloud Bridge

https://docs.hetzner.com/cloud/networks/connect-dedi-vswitch/

Setup Dedicated Server (Source)

https://docs.hetzner.com/robot/dedicated-server/network/vswitch/