iMac OS X
My iMac 2009 came with Snow Leopard, tried to download Big Sur and crashed. How can I set it back?
iMac, 10.11
My iMac 2009 came with Snow Leopard, tried to download Big Sur and crashed. How can I set it back?
iMac, 10.11
If you have the original reinstall discs that came with the iMac, use those to reinstall the OS.
If you do not have those discs, you will need to find another Mac that can run macOS 10.13 High Sierra and create a bootable USB installer that you can then use on your iMac to reinstall that macOS version.
EDIT - by the way, the 2009 iMac can run no macOS version newer than High Sierra 10.13.6
If you have the original reinstall discs that came with the iMac, use those to reinstall the OS.
If you do not have those discs, you will need to find another Mac that can run macOS 10.13 High Sierra and create a bootable USB installer that you can then use on your iMac to reinstall that macOS version.
EDIT - by the way, the 2009 iMac can run no macOS version newer than High Sierra 10.13.6
iMac OS X