in macOS I have the the drobox folder shortcut on my dock bar. When I click on it, sometimes a white icon with "icon?" name appears among my folders. I cannot delet it. Can somebody help me?
If I turn the view to grid mode, I can delete it by moving it to trash, but after rebooting mi Mac, it appears again.
That file is created by your operating system and has nothing to do with Dropbox. An Icon? file will appear in any folder where a custom icon has been specified for the folder. See here for more information.