Clean Install: Restore An App Without Installation Files

Actually, you can do it either way, and add Migration Assistant, although it's like Setup Assistant. In fact, in Setup Assistant you can transfer your entire Home folder or selected items, all third-party applications and their support files, and System preferences. All from your Time Machine backup. It's slow, though, and will take a long time depending on how much space all those files occupy in the backup.

If you just copy files, then they all need to be copied to the same locations in the newly installed system. If you use Migration or Setup Assistant (opens only when setting up a new system), then you can opt to select just the application and its support files, if you use that option, from your Time Machine backup. Or you can reinstall the application from its original media.

Does this clarify matters for you? I think I understand your query.

You've got the idea. The problem is that you cannot do that with a Time Machine backup if the file has been modified since it was first backed up. Time Machine does not actually overwrite changed files. It retains the original in a sparsebundle disk image. Changes are then backed up with links to the original. This helps to save disk space on the backup disk.

A regular file backup is when an old file is overwritten by a new version. This saves a lot of disk space but does not let you "go back in time." These are file by file backups, so you can just copy the backup file as you would any other file.

Choosing between Time Machine and a regular file backup can be difficult. Each has its merits and problems to deal with. If you only care about a handful of files, then it may be easier to put them on a USB flash drive. You did say an application is in question. My inclination would be a fresh install of the app unless you know all the files, folders, and locations of support files that are also installed and needed.

What is your computer model: To find the complete model information select About This Mac from the Apple menu. You can create a snapshot of the dialog as follows:

How to take a screenshot on your Mac

Capture, Save or Record Screenshots in Mac OS X - Help Desk Geek

OS X Screen Capture Shortcuts

(⌘⬆︎3) Command-Shift-3 Capture the screen to a file

(⌘⬆︎⌃3) Command-Shift-Control-3 Capture the screen to the Clipboard

(⌘⬆︎4) Command-Shift-4 Capture a selection to a file

(⌘⬆︎⌃4) Command-Shift-Control-4 Capture a selection to the Clipboard

(⌘⬆︎5) Command-Shift-5 Invoke new screen grabber

You can then post the image in the forum's message editor.

What version of macOS is currently installed? Which version of macOS will you be reinstalling? If you do as you initially planned, then you should use a regular file backup, rather than a Time Machine backup.

Before You Upgrade macOS

1. Fix any problems before upgrading.
2. Run First Aid in Disk Utility while booted from your Recovery HD.
3. Backup. Make a bootable clone using CarbonCopy Cloner or use TimeMachine.
4. Be sure your startup disk has 18-20GB of free space during the installation.
5. Upgrade third-party software for compatibility. See App Compatibility Table - RoaringApps. If you have mission critical software, then DO NOT upgrade until you know that software is compatible with the version of macOS you are about to install.
6. Disconnect all third-party peripherals.
7. Download the installer which will be in the Applications folder. Quit the installer after it opens, then make a copy of the installer and save it in the Downloads folder. The one in the Applications folder will be deleted after a successful installation.
8. The download is large, anywhere between 5 and 9GBs. It takes time to complete. Be patient.
9. Double-click on the installer in the Applications folder. Click on the start button to begin the installation.