Could be the cpu is being overloaded by the qos rules. Your connection is pretty small but on a large connection just turning the QoS on with no rules will cap the speed at 250mbps. This is because there is a feature that lets traffic bypass the cpu but QoS rules require it be processed.
In any case you are wasting your time setting anything on your router. The QoS settings on this router are close to worthless. In addition they can only limit the upload rates the router has no ability to even attempt to do anything with download.
You likely do not need QoS at all. Netflix and other web surfing will not impact your game. Pretty much the only traffic that would is downloads and most things like steam etc you can cap the download speed in the application so it does not use all the bandwidth.
...............a addition note since you posted this on wifi forum. Any lag in games is likely caused by using wifi and not the internet. There are no settings to solve the wifi interference issues.
I forgot to mention that i'm using ethernet connection instantly to my router, also I bought that archer vr600 like 2 weeks ago, I tried playing without QoS on and i had nonstop ping spikes that occurs in a while, for example I can get ping spike for 2 min in a row my ping goes to 600 then goes back again to 80, sometimes I can play 1 day smoothly without any issues, also my tvs are working in the internet, theres 2 cables connected to the back of my router and it's the tvs converter that's working in the internet with 5 other tvs on and with netflix, now my problem is solved, no ping spikes anymore because I changed my upload speed to 4 so I can have a little space when others using the internet, problem is that my bandwidth is now rly low only 30 mbps, on pc laptop and all phones I tested with speed tests.
I guess tha'ts worth idk.
and to the DNS servers : do I change them here in that tab?
ss:
https://prnt.sc/t3lbr3