@kabhah I am afraid not, no such settings available on the router.

@PJCwasHere Hi, thanks a lot for sharing the manual!

@luckystrikes Hi, I agree with @woozle about the LAN IPv6 DNS, if it is acceptable for you to set WAN IPv6 DNS manually, you could try Advanced->IPv6->Internet->Advanced:

@zmesh Here is the EasyMesh compatibility list: TP-Link EasyMesh Devices RE505X is listed above but marked as "PLANNED", so I suppose it doesn't support it at this moment but will do in the future.

@HareRam You could refer to this guide to find or change wireless password.

@OwenV Not very sure about Ubuntu laptop, but some Windows computer will ask for PIN instead of network security key(wireless password) when connecting to a WiFi network, usually there is another...