Factory Reset

franksmallv Said:

"Factory Reset: If I delete MacintoshHD-Data will I factory resetmy computer without deleting the OS?"

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No. You need to delete both partitions.

Reinstalling the macOS Anew:

See if this Site Helps: How to Reinstall the macOS Anew - No TMB Prior to Upgrade - User Tip. Format the hard drive with the applicable macOS, on step D.

In Depth:

Pretty much, it is a matter of:

1. Erasing: and formatting your hard drive to APFS
2. Installing: [the applicable macOS] via a USB Bootable Installer
3. Restoring: info from a Time Machine Backup, using Migration Assistant

Important: First, Back Up your Mac:

Prior to all of this, do you Create a Time Machine backup of your Mac? If so restore your Mac from it. If not, then take this as a learning experience, knowing to always create a backup of your Mac, prior to making any major changes to it (i.e. new install)

Follow these instructions to "reset" your computer: What to do before you sell, give away, or trade in your Mac - Apple Support