My 2012 iMac won’t install macOS

Hey there!

macOS Sierra is no longer eligible to be installed. See if you can install macOS Catalina, the latest compatible version of macOS with your Mac, by using Internet Recovery.

1. Start up from macOS Recovery: Turn on your Mac, then immediately press and hold these three keys until you see a spinning globe: Command (⌘), Option and R.
2. Once in Recovery, connect to a Wi-Fi network using the Wi-Fi menu (top right).
3. From the utilities window, select Disk Utility and click Continue.
4. Select View > Show All Devices in Disk Utility, and select the entry at the top of the hierarchy.
5. Click the Erase button in the toolbar, then enter the requested details:
   1. Name: Macintosh HD
   2. Format: APFS or Mac OS Extended (Journaled), as recommended by Disk Utility
   3. Scheme: GUID Partition Map
6. Click Erase.
7. When done, quit Disk Utility to return to the utilities window.
8. Select Reinstall macOS in the utilities window, then click Continue and follow the onscreen instructions.

Let us know if this works!

-Jack

If you cannot install Catalina, check if your Mac is eligible for it via:

macOS Catalina is compatible with these computers - Apple Support