Setup of 5ghz wifi as AP

i am running Netgear Nighthawk X4S R7800 as a dump AP using 5 and 2.4ghz networks... my 5ghz network is configured as
Channel: 108 (5.540 GHz)
Width 20

I am getting ping response from wifi clients to internet about ~10-20ms ... which is pretty crazy... via ethernet 5-8ms ... The issue is that lets say skype calls (video quality) is impacted etc...

Is there a way how to tune 5ghz AP? I am not able to find anything apart of the picture where the channels are depicted ...

Is it possible to say whats better for more stable performance ie width 20-40-80? What channel etc?

Appreciate any help.

What is the speed (advertised data rate) and type (xDSL, cable, fibre, wireless ...) of your Internet link?
I consider a round-trip latency of 20 ms well acceptable.

Any notable impact on phone/video calls must be caused by much higher latencies, packet loss, or a low data rate along the path between client and server. Some of these issues can be absent when a line is mostly idle, and appear when it is loaded to full capacity.

The dslreports speed test can measure speed, latency and packet loss under load (recommended settings). Could you please run it once from a wired and another time from a wireless client? You can post links to the results here if you want to discuss them.

Do the video quality problems persist when the client is connected to the router with an ethernet cable?

What is the wifi signal strength/noise (dBm) received by the client, and by the router?
Could you run any measurements just across the wireless link, for example using flent/netperf?