iMac (Retina 5K, 27-inch, 2020) can't speed up when plugged into a 2.5 G USB network card

I just upgraded the related equipment to 2.5 G. At present, everything else is normal, except that the download rate of an iMac is abnormal. Download rate: ``` ❯ iperf3-c 192.168. 11.11 Connecting to host 192.168. 11.11, port 5201 [5] local 192.168. 11.129 port 50249 connected to 192.168. 11.11 port 5201 [ID] Interval Transfer Bitrate [5] 0.00-1.00 sec 131 MBytes 1.10 Gbits/sec [5] 1.00-2.00 sec 131 MBytes 1.10 Gbits/sec [5] 2.00-3.00 sec 131 MBytes 1.10 Gbits/sec [5] 3.00-4.00 sec 131 MBytes 1.10 Gbits/sec [5] 4.00-5.00 sec 134 MBytes 1.12 Gbits/sec [5] 5.00-6.00 sec 129 MBytes 1.08 Gbits/sec [5] 6.00-7.00 sec 130 MBytes 1.09 Gbits/sec [5] 7.00-8.00 sec 129 MBytes 1.09 Gbits/sec [5] 8.00-9.00 sec 133 MBytes 1.12 Gbits/sec [5] 9.00-10.00 sec 128 MBytes 1.08 Gbits/sec ------------------------- [ID] Interval Transfer Bitrate [5] 0.00-10.00 sec 1.28 GBytes 1.10 Gbits/sec sender [5] 0.00-10.00 sec 1.28 GBytes 1.10 Gbits/sec receiver ``` Upload rate: ``` ❯ iperf3-c 192.168. 11.11-R Connecting to host 192.168. 11.11, port 5201 Reverse mode, remote host 192.168. 11.11 is sending [5] local 192.168. 11.129 port 51966 connected to 192.168. 11.11 port 5201 [ID] Interval Transfer Bitrate [5] 0.00-1.00 sec 279 MBytes 2.34 Gbits/sec [5] 1.00-2.00 sec 280 MBytes 2.35 Gbits/sec [5] 2.00-3.00 sec 280 MBytes 2.35 Gbits/sec [5] 3.00-4.00 sec 280 MBytes 2.35 Gbits/sec [5] 4.00-5.00 sec 281 MBytes 2.35 Gbits/sec [5] 5.00-6.00 sec 280 MBytes 2.35 Gbits/sec [5] 6.00-7.00 sec 281 MBytes 2.35 Gbits/sec [5] 7.00-8.00 sec 280 MBytes 2.35 Gbits/sec [5] 8.00-9.00 sec 280 MBytes 2.35 Gbits/sec [5] 9.00-10.00 sec 280 MBytes 2.35 Gbits/sec ------------------------- [ID] Interval Transfer Bitrate Retr [5] 0.00-10.00 sec 2.74 GBytes 2.35 Gbits/sec 0 sender [5] 0.00-10.00 sec 2.74 GBytes 2.35 Gbits/sec receiver ``` Points that have been checked: -Same port and same USB network card, one Linux is normal, one M1 Mac Mini is normal. It means there is no problem with the network cable and USB network card, there is no problem with the switch, and there is no problem with the iperf server -Manually download the RTL8156 driver and install it, there is no difference -Turn off Surge, iStat and other software on iMac that may affect performance, but it doesn't work Please tell me, where else may be the problem? How else can I check? -2.5 G USB network card address: https://item.jd.com/100023635636.html -Driver address: https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-usb-3-0-software