Hi PM,
we can attach files to an issue, or add files to the Files shared folder.
Yes, they are different. Attaching files to an issue will not store them in the Files shared folder.
Files attached to issue or added in shared folder will count towards the storage capacity, as do all files and content (text, code, etc) in the Backlog space.
To check the Disk Usage/Storage capacity, you can refer to our community post Overview of Space Settings.