Slow network speed on Pi4

Hi,

I’m running Home Assistant OS 6.6 on a Pi4. I wonder why I get slow network speed results.
When I run fast.com or speedtest.net within HA I get about max. 150 Mbps. Same from core-ssh:

[core-ssh ~]$ ./fast
→ 148.23 Mbps

The host-log shows eth0 correctly as 1Gbps-NIC:
10.269345] bcmgenet fd580000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off

My switch also shows the connection as 1Gbps.

Machines on the same network (Mac, Windows or Linux) show internet-speeds up to 1Gbps (max from cable-provider).

Is this a known issue or is it related to my setup? I’m running a pretty new, installation following the standard-setup-routines.