How does one remove the Dropbox link from the Navigation Pane om Windows 10?

Okay, I think I figured out how to do it. There's only one key value that you have to change, but you also have to change its permissions so that Dropbox won't change it back.

First you have to go to:

HKEY_CLASSES_ROOT\CLSID\{E31EA727-12ED-4702-820C-4B6445F28E1A}

And set the System.IsPinnedToNamespaceTree value to 0.

This will remove it from the File Explorer's navigation pane.

Afterwards, you'll need to prevent Dropbox from changing the value back.

To do this, right click the {E31EA727-12ED-4702-820C-4B6445F28E1A} key and then click Permissions. Click Advanced, and then click Add. In the dialog box that appears, type Everyone, and then click OK. Change the type to Deny, and make it apply to This key only. Click Show advanced permissions, and check the Set Value box.

Afterwards, click OK and Dropbox should no longer be able to modify that value. Hopefully Dropbox or Microsoft will make this kind of thing easier someday.