whne you make it private, it will be visibl to the user it was created by, and you can see it in bubble.io with current user being that user, see is it not visible like that
When user is not allowed, the URL shows a Permission denied error. In my case, the user is allowed to view the file, but when redirect to URL, the broken image appears (as in my screenshot)
Did you check the URL? When you are redirecting to a Bubble stored file URL, you need to prefix the URL with https: in order for it to be parsed correctly