@MarkSc 

Hi,

In order to get the most accurate answer please confirm the actual router model you have.

TP-Link sells at least four different "AX5400" class routers, like the  Archer AX72 ,   Archer AX72 Pro ,  Archer AX73  and  Archer AX75 .

In case your AX5400 Wi-Fi 6 Router is a different brand than TP-Link, then please also let us know the actual model name.

However, the chances of a TP-Link range extender being able to build a Mesh Wi-Fi network with a router of another brand are very small. 
TP-Link's own "OneMesh" will not work together with any router of another brand. 
Some of TP-Link's range extenders also support the official "EasyMesh" standard, but so far the other brands haven't released many devices that support it. 

  @woozle  sorry needed to find the bill l. It is a AX73

  @MarkSc 

If you are looking for the type of wireless range extender that is small and plugs directly into a wall socket, then the models RE700X, RE705X and RE715X would be good matches for your Archer AX73 router. They are EasyMesh-compatible and provide AX3000-class speeds.
There doesn't seem to be a dual-band AX5400-class range extender on offer currently.

However, another possible route to go would be to get a second Archer AX73 router and use that as the "Mesh Extender". That should be the best match actually, because the Wi-Fi specs would match exactly.
When building an EasyMesh network between two Archer AX73 routers you would even have the choice of either connecting the two routers wirelessly or by wire (also known as "Ethernet Backhaul").