One-Arm Sniffer - Filter for only untagged packets?

Hi,

we have a One-Arm Sniffer interface where we want to filter to only sniff untagged traffic. The port that is being mirrored contains both untagged and tagged packets. I can only see the option to specifically choose which VLAN you want to sniff but not the other way around.

Anyone that have an idea of how we could solve this?

BR Robin