@RodrigoEA 

Can you confirm if the QoS on the AX6000 is disabled? Try to disable the QoS, ensure it is on the Standard mode, ensure there is no device in high priority. Or you may just reset the AX6000 to factory defaults, then reconfigure it to connect to the internet, leave other advanced settings by default, that will also help with this check, thanks.

@RodrigoEA 

It is suggested to reset the AX6000 to factory defaults, that will clear all the settings on the router and will help locate if the issue is related to the firmware or to the wrong configuration.

After the factory reset, please reconfigure the basic parameters on the AX6000, leave all the advanced settings on it, then test the speed again.

Please show us the link speed on the note 20 ultra, ensure the link speed is normal when connected to the 5G network. You can also test the speed on other 5G devices.

If that still doesn't help, please try to modify the 5G wireless settings on the AX6000, such as wireless channel and channel width. It is suggested to run a Wi-Fi analyzer to find a clear channel, then change the channel width to 80MHz, reboot the router and reconnect to the wireless network, then confirm.