Try setting Band to "5Ghz (AC Only)" and Channel to "Auto"

Tap on the Wifi name on your J7, I think it should show you the Link Speed. What is it?

Sorry, not sure why it connects at only 65Mbps. You should be connecting at 300-400 at least. Any other wifi devices/laptop you can try?

Are you very close to the router when testing?

If you are, one last thing to try, turn down the RGX4400 radio power to 35%. Power cycle the RGX4400 and try again.

Can you test on PC with TM speed test:

http://speedtest.tm.com.my/tmspeedtest.html

On 2.4, you probably get max 80-100Mbps. Most/All phones will only use 20Mhz even if you set the router to 40Mhz. This is assuming 2 streams. I think the J7 Pro should be 2 streams.

Connect to 2.4 and look at your link speed.

As as guesstimate, the max speedtest you can get is usually 1/2 to 2/3 of the link speed.

Your PC is quite far from the RGX4400? The Speedtest you did just now for the PC is quite OK. Don't expect too much from 2.4 and the tiny DWA-131.

Be aware that 5Ghz not so good for even slightly moderate distance. It's hard to say without knowing what's between your PC and the router.

Any brand will do. I don't use Asus so can't recommend anything from them. Personally I use Mikrotik.

Better buy Cat6 cable to connect router directly with you PC.

Wired network is king 100% ...this all USB (wifi)...hmmmm. ..you will never get proper speed.

Btw,
DIR-867 is arround RM600 (+)
Maybe Tenda AC18 (~RM280) or TP-Link C7 V.5 (~RM350).

Not true. They gave the same B S. when my turbo-ed 800mbps could only get 200mbps. It turns out that I had to switch to a cat 6 cable between router and b.t.u. and re-enable a setting on my router.

I am getting 830+ Mbps after the fix.

CAT-5e is from router box?
Tried with CAT6 cable?
(also try reboot after 10 mins shutdown)

If still below 100Mbps, either your BTU was wrong configuration 10/100Mbps instead of 1000Mbps, or you are really still in pilot's victim...

we did, but he don't want cable things ...

Yes, what is your BTU model exactly? 'Silver box' ain't informative you know....

Not sure why you are complaining, when all the seniors have taught you, me included, to change router, or test via wired. You seem to just keep doing the same thing over and over and over again, and expecting the same results  

Aiyo, your device has limitation and please use the correct term of Bytes and bits. You are confusing us..
Just change router, you use Cat-6 cable now also doesn't help much.

Probably extra @unifi at wireless?
Yes.
Yup.
BTU = no problem
Router = no problem

Let focus on your desktop computer wifi chip.
You mentioned your desktop wifi chip can only support 2.4Ghz band. May I know your desktop wifi chip model?

edit:
Next, can you install https://play.google.com/store/apps/details?....analyzer&hl=en on your Samsung J7 Pro phone? Please post the screenshot of how many 2.4Ghz hotspot around your area.

Asus Rtn12hpb1 = doesn't matter wifi or lan, the top speed you will get is 95 - 97 Mbps. WAN port is Fast Ethernet 100Mbps (This is the main limitation)