HOW TO Create a clean install of macOS

1 Back up your Mac

We can’t stress this enough: make sure that you have a full backup of everything you want to keep on your Mac, because we’re going to do what’s called a clean install — that’s when you create a factory– fresh version of macOS.

2 Download macOS

We need the macOS installer from the Mac App Store. Unfortunately, a bug means the download often fails for Big Sur. To get around that, launch Terminal and enter: softwareupdate --fetch-full-installer to download the installer.

3 Plug in USB

Now make a USB bootable installer. For that, you need a 16GB or larger USB flash drive and the macOS installer. The latter must be in your Applications folder. Plug in the USB flash drive; if you’ve closed Terminal, open it again.

4 Make a bootable drive

You now need to enter the appropriate code into a new Terminal window. The commands vary according to each macOS version; the different commands are all helpfully listed on the Apple website at https://tinyurl.com/macbootusb.

5 Time to wait

Press Enter, and now you can step away for a bit: this part takes some time. Terminal will keep you updated about its progress until the bootable USB drive has been created. You can then quit Terminal and shut down your Mac.

6 Reboot your Mac

Restart your Mac and if it’s an Intel one, hold down Opt until you see the boot options menu; on an M–powered Mac, press and hold the Power button until the menu appears. On either kind of Mac, you should see the macOS Utilities screen.

7 Change the security settings

On some M–powered Macs you may get a security error. Reboot your Mac, hold down Cmd+R for Recovery mode, select Utilities > Startup Security Utility, and enable Allow Booting From External Media. Retry step 5.

8 Erase your Mac

Select Disk Utility from the options, choose Macintosh HD (or whatever you want your main drive to be called) as the disk name and select APFS as the file system. Now choose Erase. Note: This removes everything from your drive.

9 Install macOS

Once Disk Utility has finished formatting your main drive, you can quit Disk Utility. This will take you back to the macOS Utilities screen. You can choose the Install macOS option by selecting the bootable USB drive from the options.

10 Start from scratch

Congratulations: you now have a pristine copy of macOS, free from the chaff that accumulates in any operating system over time. All you need to do now is restore your apps and files from your backup and pick up where you left off.