See my reply to you on other thread. VLAN settings and because of 2.4GHz interference, as your router does not support 5GHz AC. Why did you get that router anyway? It is not much better than the TRG-212M, and it has very basic hardware.

Fair enough. The owner is an idiot then. I have a feeling that he is paying more for less lol. Anyway, fair enough. That router is sufficient for your needs,

Bro, every router from TP-Link has the Unifi mode. You are looking for it at the wrong place. Go to your router, look for ‘Network, then ‘IPTV’, then select mode ‘Malaysia-Unifi’. You will be be able to use it as a router then. Remember to set Operation Mode to Wireless Router to use it as a main router. By the way, what version are you using? Look at the box and see the version. Get the latest firmware here: https://www.tp-link.com/my/download/TL-WR840N.html

If you do update the firmware, you have to reconfigure it again, so have your PPPoE username and password ready, and remember to set ‘Malaysia-Unifi’ mode again.