Sorry, I was a bit short in my description.
Here is what I did so far:
I created a bridge br10, it is active and has the IP 192.168.199.2/24 without adding any network adapters as members (that share is only for the VM)
To the VM I have added a NIC (using virtio) and attached it to br10. The NIC is visible and activated within the VM with 192.168.199.3/24.
From the truenas host, I can ping the bridge but not the ip of the VM. The other way around I can ping from the VM the adapter I created (obviously) but not 192.168.168.2 on the bridge.