If you navigate to a non-existent item
e.g.
https://my-instance.atlassian.net/browse/BOGUS-6
or an item that has been deleted:
https:// my-instance .atlassian.net/browse/REALPROJECT-6

The resulting page says, in both cases:

We can't show this project.
You don't have permission to view it, or it doesn't exist. Contact your admin to request access.
[Request access]

This is misleading. There is no item to request.
Now, if you're requesting a bogus project name like the "BOGUS" example above, I suppose it's OK to presume that the non-visibility of the item is because the user doesn't have access to the Space/Project in question, and telling the user that the Project is not found would give away some information.

But for a project like REALPROJECT that I have access to, it should say "no such item".