@Giff If you want to use VR2800's LAN4 port as WAN port you have to switch its 'Operation Mode' to 'Wireless Router Mode':

@Tonylr You can use any RE to expand further your wireless coverage, but go through this FAQ - Part 3 - Q3.6/A to see how you can do that more efficiently.

@Piie OneMesh doesn't support an ethernet backhaul - OneMesh FAQ - Q5/A5. OneMesh is not supported by Omada EAPs either. If you want, you can use an ethernet cable to connect the RE505X to your AX20...

@Reckless Use this video guide for more detailed steps for setting up the extender.

@FrustratedXuser Make sure that C6 is in 'router mode' and use this guide for configuring the WDS feature (i.e. wireless repeater).

@Rajit Go through this thread to learn for some considerations when daisy-chaining range extenders. You can go through this FAQ - Part 3 - Q3.6/A as well.