Erase & Reinstall macOS
Complete guide to wiping and reinstalling your system
Bottom lineDo this last, after every other check passed. Back up first, then use System Settings > General > Transfer or Reset > Erase All Content and Settings (macOS Monterey or later on Apple silicon or T2 Macs). Only fall back to Recovery Mode and Disk Utility if that option is missing. A clean install removes the previous owner's data and any leftover profiles.
Backup Your Data
Use Time Machine or manually back up important files
Use the Modern Reset Option First
On macOS Monterey or later with Apple silicon or a T2-equipped Mac, go to System Settings > General > Transfer or Reset > Erase All Content and Settings
Use Recovery Mode If Needed
If Erase All Content and Settings isn't available: 【Apple silicon】Shut down, then press and hold the power button until you see 'Loading startup options'. Click Options > Continue 【Intel Mac】Restart and immediately hold Command (⌘) + R until the Apple logo appears
Erase the Internal Disk Carefully
In Recovery, open Disk Utility. Select Macintosh HD. If you see Erase Volume Group, use that; otherwise choose Erase and keep APFS unless Apple shows a different requirement
Reinstall macOS
Quit Disk Utility, choose Reinstall macOS, and follow the prompts. If you're selling the Mac, stop at the setup assistant and don't sign in again