@vNetwork 

1. What is the distance between your main Deco and Win11 PC? It is suggested to move Win11 PC closer to your main Deco, as the wireless coverage of 5GHz and 6GHz are different.

My PC and the Deco are in the same room. The distance between them is around 5m. It is very open with just a sofa in between.

And you may check whether your Win11 PC is connected to your 6GHz band of your main Deco on Deco app following this guide. 

Yes, I am on 6GHz.

2. Please refer to the guide to check link speed on your Win11 PC and share the screenshot here.

3. Did you test speed via www.speedtest.net?

Yes.

Additional:

1. Did this ----> Or, change to standard, remove all priorities and set bandwidth to 1000Mbps.

2. Did this ----> Turn off the UPNP feature and SIP ALG feature in the Deco App Under: More > Advanced > NAT Forwarding.

  @vNetwork 

I got the Archer TXE70UH USB WiFi adapter to work on my Linux Mint OS on the same PC. It is getting 781 Mbps download speeds.

https://community.tp-link.com/en/home/forum/topic/719830?replyId=1450414

I am still trying to figure out why it runs at half the speed on Windows 11. I have uninstalled all the ASUS software on my Windows 11. I am not exactly sure what software issue is causing this WiFi 6E to run so much slower than on Linux Mint.