I only have experience with networkd as the renderer not NetManager, so I don't know the value of this answer.

Save /etc/netplan/01-network-manager-all.yaml somewhere, so that you can revert if things do not work.

Create /etc/netplan/01-netcfg.yaml (gateway address assumed):

# This file describes the network interfaces available on your system

# For more information, see netplan(5).

network:

  version: 2

  renderer: networkd

  ethernets:

    enp4s0:

      dhcp4: no

  bridges:

    br0:

      interfaces: [ enp4s0 ]

      dhcp4: no

      addresses: [192.168.2.15/24]

      gateway4: 192.168.2.1

      nameservers:

        addresses: [1.1.1.1]

      dhcp6: no

      link-local: [ ]

      parameters:

        stp: true

        forward-delay: 4

Do:

sudo netplan apply

Go to /etc/libvirt/qemu/networks. There should be a host-bridge.xml file. Save a copy:

sudo cp host-bridge.xml host-bridge.xml.original

If you do not have a host-bridge.xml file, my original was:

doug@s19:~/config/etc/libvirt/qemu/networks$ cat host-bridge.xml.original

<network>

    <name>host-bridge</name>

    <bridge name='br0'/>

    <forward mode="bridge"/>

</network>

Runs these commands:

virsh net-define host-bridge.xml

virsh net-autostart host-bridge

virsh net-start host-bridge

virsh net-list --all

In case of having issues and needing to undo, be aware of:

virsh net-destroy br0

virsh net-undefine br0

Example:

doug@s19:~/config/etc/libvirt/qemu/networks$ virsh net-list --all

 Name          State    Autostart   Persistent

------------------------------------------------

 host-bridge   active   yes         yes

Example:

doug@s19:~/config/etc/libvirt/qemu/networks$ sudo cat /etc/libvirt/qemu/networks/host-bridge.xml

<!--

WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE

OVERWRITTEN AND LOST. Changes to this xml configuration should be made using:

  virsh net-edit host-bridge

or other application using the libvirt API.

-->



<network>

  <name>host-bridge</name>

  <uuid>d474d859-8448-4055-9fc0-bb0b6cb83c34</uuid>

  <forward mode='bridge'/>

  <bridge name='br0'/>

</network>

Now, modify any existing VMs to use the bridge:

Note: There is probably a way to do this step using virt-manager, however I do not use it and do not know how.

Use virsh edit and change your interface definition lines to use bridging instead of what is currently being used. Something like this:

Before:

<interface type='network'>

  <mac address='52:54:00:06:8d:b0'/>

  <source network='default'/>

  <model type='virtio'/>

  <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>

</interface>

after:

<interface type='bridge'>

  <mac address='52:54:00:06:8d:b0'/>

  <source bridge='br0'/>

  <model type='virtio'/>

  <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>

</interface>

For creating a new VM, and depending on your method, something like:

virt-install -n serv-jj -r 8192 

--disk path=/home/doug/vm/serv-jj.img,bus=virtio,size=50 

-c jammy-live-server-amd64-2022-04-21.iso 

--network bridge=br0,model=virtio,mac=52:54:00:27:1c:6e 

--graphics vnc,listen=0.0.0.0 --noautoconsole -v --vcpus=4 --cpu SandyBridge 

Examples with 3 VMs running:

doug@s19:~$ ip addr

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

    inet 127.0.0.1/8 scope host lo

       valid_lft forever preferred_lft forever

2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master br0 state UP group default qlen 1000

    link/ether 3c:7c:3f:0d:99:83 brd ff:ff:ff:ff:ff:ff

3: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000

    link/ether 3c:7c:3f:0d:99:83 brd ff:ff:ff:ff:ff:ff

    inet 192.168.111.136/24 brd 192.168.111.255 scope global dynamic br0

       valid_lft 81610sec preferred_lft 81610sec

4: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master br0 state UNKNOWN group default qlen 1000

    link/ether fe:54:00:22:2f:dc brd ff:ff:ff:ff:ff:ff

5: vnet1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master br0 state UNKNOWN group default qlen 1000

    link/ether fe:54:00:60:ea:3e brd ff:ff:ff:ff:ff:ff

6: vnet2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master br0 state UNKNOWN group default qlen 1000

    link/ether fe:54:00:60:ea:5e brd ff:ff:ff:ff:ff:ff

doug@s19:~$ networkctl

IDX LINK   TYPE     OPERATIONAL SETUP

  1 lo     loopback carrier     unmanaged

  2 enp3s0 ether    enslaved    configured

  3 br0    bridge   routable    configured

  4 vnet0  ether    carrier     unmanaged

  5 vnet1  ether    carrier     unmanaged

  6 vnet2  ether    carrier     unmanaged

doug@s19:~$ brctl show

bridge name     bridge id               STP enabled     interfaces

br0             8000.3c7c3f0d9983       no              enp3s0

                                                        vnet0

                                                        vnet1

                                                        vnet2

Not covered herein: How to set the static address of 192.168.2.16 on the VM, because the VM was stated to be FreeBSD and I do not know how.

References:

https://netplan.io/examples/#configuring-network-bridges

KVM Network Bridge to assign Static IP