@Piergiorgio 

Hello, please help verify some details, and we will try to fix it together:

1. May I know who is your ISP? What is the speed you can get when you connect a computer directly to the modem?

2. Without any devices connected, please connect one computer to the AX6000 directly and go to speedtest to run the test for 3 times and show us the screenshots of the test results.

And please tell me the wired link speed at that time, how to get that? You can refer to the below link.
https://www.tp-link.com/faq-2265.html

3. What is the speed tested on the Tether app? It might be different from that on your computer, we may think the Tether speed is more like the connection speed between the router and your internet, which would be different from the speed you can get on the computer, while we can verify it first.

4. Do you enable any QoS setting on the router? Kindly show me the QoS setting page on your AX6000, try to disable it then check again.

Good day.

@Piergiorgio 

Hi, thanks very much for getting back.

Have you confirmed if there is any QoS setting on the AX6000? Try to disable it and reboot it, then confirm again.

@Piergiorgio 

Hello, can you refer to the below link to check if you can update the driver for this laptop, even though the issue is different, we hope you give it and try:

https://community.tp-link.com/en/home/forum/topic/234446

BTW, we would like to escalate your case to our engineers, and they will help follow it up, if you are willing to do further analysis, please check your inbox and respond.  

Good day.