does this apply to iMac computers too?

If you have followed all the troubleshooting steps on what to do if a question mark appears, that indicates the Mac cannot find it's startup volume, this means your hard drive may have failed, the hard disk has been completely erased etc. You can use Internet Recovery if the computer is a 2012 or later if the drive was simply erased or you can boot into the Recovery Partition and install Mac OS from the RP.

However, if it is a hardware failure there is nothing a help forum can do other than to tell you your next stop is to visit your local Apple Authorized Service Provider to have the computer professionally diagnosed and then you can select your repair option.

Did you boot into recovery? Holding Command + R keys immediately after hitting the power button to boot or the restart menu option?

What happened?

You will have the folder with the ? until you install a Mac OS. That image tells you that the computer cannot find its startup disk, so you can't boot from it. That is why you need to either boot from a plugged in external clone or the built in recovery options.

Yes. The instructions in it apply to all Macs which shipped with 10.7 or newer.

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Did you follow any of the suggestions offered in the Apple article link above your post? And yes, it does apply to Macs.