@Gary-M
Hello, do you mean only the 2.4GHz connection is slow? If that is the case, it's quite possible that the 2.4GHz band around you is highly congested. You can check that by installing an app like Wi-Fi Analyzer on your phone or laptop and test, then set a channel with less congestion according to the test results on the AX73.
Check this troubleshooting article for more suggestions:
https://www.tp-link.com/support/faq/2170/
BTW, what is the wireless link speed when you connect to the 2.4GHz network? If it is a Windows laptop, you can follow the below guide to find it out:
https://www.tp-link.com/support/faq/2265/