Nighthawk Nighthawk X6 R8000 ac3200 router channels problem

Channels 100-140 are dfs channels. If you live in an area with military radar or weather radar, they might be in use and unable to be selected. 

https://kb.netgear.com/000060371/What-is-Dynamic-Frequency-Selection-and-how-does-it-work-with-my-NETGEAR-device

In apartment living, its challenging because 2.4ghz is almost pointless. To start with its a slow network and sensitive to interference. When I used to live in an apartment, I made sure to only buy devices that supported 5ghz because it was so worthless to use 2.4ghz. So in terms of the 2.4ghz, I'd come close to writing it off. 

I'd focus on the 5ghz channels. Good thing about 5ghz is that it doesn't broadcast as far as 2.4ghz and it can't broadcast through as much materials. Plus, because its so much faster, if you are streaming/gaming, it can download the data at a quicker rate so the period of time where there's inference, it shorter. Meaning its more efficient. So even through you can see other 5ghz channels, usually there's a lot less interference from them.