Make Galaxy S7/Android install drivers for MTP (Nougat, Win 7)
Try this:


Open the dialer
Type *#0808#, should open the USBSettings menu.
On the window that comes up, on USB, tick AP. On USB Settings tick MTP + ADB
Reboot the phone. Windows should now install drivers and the phone should be detected in debugging mode.





  Can I make Nougat's developer settings' USB debugging default to PTP? Every time I unplug the phone, Android sets it back to MTP.


Try: 


Pull down the notification panel 
Then touch the USB sticky notification
Select Tranferring media file (= MTP)


Your phone should remember this setting and never forget again :D



UPDATE:

Try *#9090# and select DM/DUN over HSIC 

Also try revoking the USB debugging authorizations in the Developer options. Works fine in most time.