I seem to have found the problem! I saw an article that introduced that openwrt’s 5G wifi is too slow because the router’s CPU usage is too high. Then I saw the switch “Enable real-time speed and traffic statistics. This requires higher CPU load.” on the CLIENTS page of MT1300, I turned it off and tested the speed again

 .\iperf3.exe -c 192.168.1.1 -b 1G
Connecting to host 192.168.1.1, port 5201
[  4] local 192.168.1.9 port 5233 connected to 192.168.1.1 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  47.6 MBytes   399 Mbits/sec
[  4]   1.00-2.00   sec  57.1 MBytes   479 Mbits/sec
[  4]   2.00-3.00   sec  65.4 MBytes   549 Mbits/sec
[  4]   3.00-4.00   sec  55.5 MBytes   465 Mbits/sec
[  4]   4.00-5.00   sec  55.9 MBytes   469 Mbits/sec
[  4]   5.00-6.00   sec  70.4 MBytes   590 Mbits/sec
[  4]   6.00-7.00   sec  57.9 MBytes   486 Mbits/sec
[  4]   7.00-8.00   sec  47.8 MBytes   400 Mbits/sec
[  4]   8.00-9.00   sec  57.2 MBytes   480 Mbits/sec
[  4]   9.00-10.00  sec  51.9 MBytes   435 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.00  sec   567 MBytes   475 Mbits/sec                  sender
[  4]   0.00-10.00  sec   566 MBytes   475 Mbits/sec                  receiver

iperf Done.

Speed ​​has increased! It seems that the CPU usage is really related to the network speed! Maybe I should uninstall all the software I don’t need on the MT1300 to reduce CPU usage!

By the way, it’s an exaggeration that a switch that shows the internet speed has such a big impact on internet speed!

@sparky66 @LupusE