dslrdashboard.info

What camera did you use?
What where the exact settings? Maybe a screenshot.

If it does not support the 'Smart remote control' Playmemories camera application then it will not work.

- enable wireless on your D7500 - connect your Pixel wireless to the D7500 - start qDslrDashboard and press the 'Nikon wireless' button * be sure that no other device is connecting to the D7500 wireless * be sure that the Nikon WMU or Smartbridge applicaitons are not running on your Pixel * be sure ...

No it is not, on iOS devices only wireless connection is possible.
USB is available on Android and the desktop version (Windows, Linux, macOS)

You should long press the qDslrDahboard capture button after it will turn red, after that the image is downloaded after the capture.

You can download the images from camera SD card in the qDslrDashboard 'Image gallery'.
Not sure if that is what you mean.

On what platform do you use it? Please contact me with the support email.

Unfortunately not, this is by default on Nikon cameras and can't be changed

In qDslrDashboard settings disable the 'Use Android native USB access' option.
You need to use an USB OTG adapter.

To use the camera built in wireless the controlling device needs to directly connect to the camera so there you can't wireless range extension.
You could connect your camera with USB to a portable wireless router running ddserver and use it's wireless to control the camera with qDslrDashboard.