Validate your QoS implementation: For QoS to be effective, the DSCP value set by the GPO needs to be present at both ends of a call. By analyzing the traffic generated by the Teams client, you can verify that the DSCP value isn’t changed or stripped out when the Teams workload traffic moves through the network. Preferably, you capture traffic at the network egress point. You can use port mirroring on a switch or router to help with this.

 Validate your QoS implementation: For QoS to be effective, the DSCP value set by the GPO needs to be present at both ends of a call. By analyzing the traffic generated by the Teams client, you can verify that the DSCP value isn’t changed or stripped out when the Teams workload traffic moves through the network. Preferably, you capture traffic at the network egress point. You can use port mirroring on a switch or router to help with this.

https://learn.microsoft.com/en-us/microsoftteams/qos-in-teams#validate-your-qos-implementation