[Windows 10 Mobile Apps. and Games] juanitogan:
I have the same OS: Lumia 830. Windows 10 1607. Build 10.0.14393.1480

I have been struggling through similar issues so I went back and read every post since the last release. And, what I learned was, basically, as great as this tool is, you have to read more than 100 posts to learn the basic quirks of it.

I got pretty lucky, in general. Before any other tools or versions here, I installed InteropTools_L_2.0.54.0_x86_x64_arm.appxbundle and it's dependencies through Windows Device Portal without issue. ("Interop Tools (Preview)" appears as an app in the apps menu and not as a system setting. Not sure where you got different info on that.) I guessed at NOT installing the "extensions" attached to that #887 release post even though it is totally unclear what they are there for and what to do with them. For all I knew, coming into this with no background on it, they were part of the dependencies. But I had some hints from some other pages that they may not be needed so I skipped them at first.

The opening screens in Interop Tools are terribly confusing and somewhat suspicious but I slogged through them and somehow chose "THIS DEVICE, Connects to this device natively..." as the right answer (the first option didn't feel right because of something about provider extensions and that sounding somewhat like the things I skipped installing). These first two options should be reversed, in my opinion, if the second really is the preferred new method.

Then, I too, was having trouble understanding the Interop Unlock screen and the toggles that don't seem to work. I just wanted access to the file system so I wasn't planning on using the Restore NDTKSvc feature at first (not sure if that's a correct determination). But, nothing else seemed to be working, so I then tried Restore NDTKSvc. It, too, didn't seem to want to work... but it eventually stuck... not sure how... I remember rebooting more than once. What I later learned here is that you should give it several seconds to work... if it's going to.

Still, however, nothing else seemed to work in the Interop Unlock screen so I reverted to installing those extensions and opening the app with the first "THIS DEVICE" option. I found Interop Unlock to be not much better that way except that the toggles turned themselves off much slower. So slow, sometimes, that Interop/Cap Unlock would appear to get stuck on... but that was an illusion. The next two options are always much quicker to turn themselves off. What I later learned here is that these "switches" work even if they revert to the off state. In fact, they may not even be binary state features but, rather, irreversible features that you enable. I learned later that that is true with Restore NDTKSvc, so maybe these others as well.

I also learned from reading all those posts that Full Filesystem Access is supposed to provide an edit field for setting MTP Root Path. I never see this field. Presumably, because the toggle doesn't stay on. Thus, I learned I can accomplish the same thing by editing:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MTP\DataStore

...from it's default value of C:/Data/Users/Public to whatever. (Although, I never gained write access to D:\WPSystem\AppData like I had hoped. Just decrypted read. Any ideas here anyone?)

So, assuming these "switches" work in spite of their UI glitches (toggles are probably not the best widget choice or, at least, disable the ones than cannot be undone), I tried the above edit to DataStore in the registry and it worked! Who knew?

So, all I can really tell you, [MENTION=8422957]Alec.McT[/MENTION], is good luck and I hope my tl;dr story helps somehow.

To everybody else, it would help some of us a great deal if the top post included more details on:

What these "extensions" are, what versions they apply to, when to use them, and why?

What a "provider" is and which one to choose and why?

Should I fear the security step? What's it really doing with my PIN?

What the known UI quirks are such as these toggles that turn themselves off and the MTP Root Path that doesn't show

What features require patience because they take a few seconds, and how much?

What features cannot be reverted such as Restore NDTKSvc

What features do and don't require RestoreNDTKSvc

Is [MENTION=939315]dxdy[/MENTION] correct that some earlier versions of Windows 10 Mobile need earlier versions of Interop Tools?

Otherwise, "Thank you!" to [MENTION=7651894]gus33000[/MENTION] for this powerful and useful tool. Keep slugging away at it! I hope my critiques help.