Are you saying your "Internet Speed Test" isn't getting good Wifi speeds?
What do the connection speeds say for your Devices under View List from the AX86U router's main Network Map page?
On the AX86U router I'm using right now it shows I have devices connected at 5Ghz ranging from an estimated 300 to 800+ Mbps. It all depends on the quality of the radios those devices have, the open 5Ghz channels that are available in your area, the bandwidth you are getting on those channels (20, 40, 80, 160Mhz), whether they are N, AC or AX, how many antennas they have, how far the devices are away from the router, the materials in the structure you reside in (concrete walls, wood, plaster, etc..) and the objects that the 5Ghz signal can reflect off of. All of this can effect that signal.
There are so many variables that can effect this and really 300Mbps isn't a bad speed in general. If you are downloading and uploading 4K video content at the same time via Wifi then of course you want a higher maximum throughput. If you want to get maximum Wifi speeds you are going to have to experiment more with the settings. Internet Speed Test isn't the best way to test it either since that can vary from one test to the next and especially over a 1Gbit connection. A better test would be transferring content via the router's Wifi from another device within your local network and if you require stable high Wifi 6 throughput over longer distances you should be using two AX86Us.