I'm doing this on a couple of machines. Only running NFS, Plex (looking at a Jellyfin migration soon), Home Assistant, LibreNMS and some really small other stuff. Not using VMs or LXC due to low-end hardware (pi and older tiny pc). Not using containers due to lack of experience with it and a little discomfort with the central daemon model of Docker, running containers built by people I don't know.
The migration path I'm working on for myself is changing to Podman quadlets for rootless, more isolation between containers, and the benefits of management and updates via Systemd. So far my testing for that migration has been slow due to other projects. I'll probably get it rolling on Debian 13 soon.
Are you specifying bandwidth (-b) on the iperf UDP test? It defaults to 1M if I recall correctly, which would explain the result.
If not, try
-b 10M
or-b 0
for unlimited (the behavior used for TCP).