An app — a backup tool, an antivirus, a sync client, or the Terminal — has told you it needs Full Disk Access, and the list it sent you to does not contain it.

Here is where the setting is, what it covers, and the step that makes it actually take effect.

Where it is

System Settings → Privacy & Security → scroll to Full Disk Access.

There is no URL that opens it directly. Several of the privacy sections have their own anchors, so an app or a script can link straight to Screen Recording or Microphone; this one does not vend a token on current macOS. An older Privacy_AllFiles anchor circulates in lists of these URLs and it no longer does anything.

The closest you can get is the pane, and then a scroll:

open "x-apple.systempreferences:com.apple.settings.PrivacySecurity.extension"

Granting it

1. Open that section.
2. If the app is already listed, switch it on.
3. If it is not, click +, then find it — usually in /Applications — and add it.
4. Quit the app completely and open it again.

Step 4 is not optional here. Full Disk Access is applied when an app starts, and an app that was running when you granted it carries on with exactly the access it had before. macOS will usually offer a Quit & Reopen button; take it.

What it covers that ordinary file access does not

This is the part worth understanding, because the name oversells it in one direction and undersells it in another.

Apps can already read files you hand them — anything you open, drop on them or choose in a file dialog. Files & Folders access extends that to your Desktop, Documents and Downloads without asking each time.

Full Disk Access is a different category. It covers the places macOS protects from everything by default:

• Mail, Messages and their attachments.
• Safari's browsing data, history and cookies.
• Time Machine backups.
• Other apps' private data containers, in ~/Library/Containers and ~/Library/Application Support.
• System-level locations that ordinary file access does not reach.

So the meaningful question is not whether the app needs to read your files. It is whether it needs to read your mail, your messages and every other app's private data. For a backup tool the answer is genuinely yes, because a backup that skipped all of that would not be a backup.

The Terminal is a special case

Granting Full Disk Access to Terminal — or iTerm, or any other shell — is common advice for administrative tasks, and it is worth understanding exactly what it does.

It does not grant access to the Terminal. It grants it to everything you run inside the Terminal, for as long as the permission is on. Every script, every downloaded tool, every command someone told you to paste, all of it inherits it.

That is fine for a task you are doing now. It is worth switching back off afterwards, which almost nobody does.

The same applies, more quietly, to anything that runs other code on your behalf — automation tools, package managers, development environments.

The app is not in the list and + does not find it

Three common reasons:

• It is a command-line tool, not an app. The + dialog shows applications by default. Use ⇧⌘G in that dialog to type a path — /usr/local/bin/, /opt/homebrew/bin/ — and pick the binary itself.
• It is a helper inside another app. Some software wants the permission for a helper buried in the app bundle rather than the app you see. The app's own documentation should say so; if it does not, grant it to the app first and see whether that is enough.
• You have two copies. The permission is tracked per copy. If you granted it to the one in Downloads and you are running the one in Applications, nothing will work and nothing will explain why. Delete the spare.

Turning it off again

The switch works both ways, and revoking costs nothing permanent — the app loses the access and will ask again if it needs it.

It is worth reading this list once in a while, the way it is worth reading the Accessibility one. Backup tools you replaced, antivirus you uninstalled and Terminal grants from a task two years ago all tend to still be sitting there switched on. See what Accessibility permission grants for the same argument at more length.