Welcome to our forum @marzab! English is fine. On the wifi light, it's normal behaviour. As long as the light flashes every now and then, as opposed to blinking on and off steadily. 

About the Extra Wifi, are you sure your computer can see 5GHz networks? If you aren't sure please let us know what wifi hardware you have in your computer. That way we could take a look.

Hello, yes my computer sees the 5ghz network. As for the flashing wifi light in the modem. Recently, I noticed that it is flashing all the time. The internet is there.
Is this the way it should be? I have already changed the internet cable
(the red one) but still blinks almost all the time.
The second thing is why does it change my internet channel from time to time? For example, I set up 5ghz internet on channel No. 104 and after some time I have changed to channel 64?

@marzab the light flickering is completely normal. Nothing to worry about! 

About the channel, again don't worry. configuration may change depending on what's needed to give you best services. 

It's a bit weird, because in the previous post I had it written that flashing is normal from time to time, and I have to worry about it flashing all the time.  Right now I am flashing almost all the time.  With much greater frequency.  And is it possible to set the channel rigidly so that it does not change?  I must admit that on channel 104 it works much better.

@marzab we try to do things automatically as much as possible. But to change it yourself you can log into the modem. If you use the Wifi Manager it will choose the best channel for you. 

The light will indicate there is a problem either by going red, orange or turning off completely. Flashing lights are not a problem in this case.