GL- AR750S-EXT - Xbox - DNS isn't resolving Xbox server names

I have connected devices to my router. All devices have internet connection except for the Xbox. The Xbox continues to tell me “DNS isn’t resolving Xbox server names”. I received this if I was plugged into LAN or connected through Wireless on 5g and 2g. I am able to connect the Xbox if I use the router as a repeater instead of connected through the WAN port. Any help on how to connect the Xbox through the WAN/LAN setup?

I have no idea of what is the reason but can you set DNS manually in your xbox?

For example like what this article said