need help on disc repair. iMac cannot find ir

If Disk Utility can not see the disk, then it has most likely failed.

Best bet, is to schedule a service appointment at your local Apple Store or Apple Authorized Service Provider.

To do that, go to > https://getsupport.apple.com/repair-locations?locale=en_US

There is no 2016 model iMac, just a 2015 and a 2017. You can get the exact model by entering the system serial number (found on the bottom of the stand) into the check coverage area found here:

Check Your Service and Support Coverage - Apple Support

Try booting the iMac into Internet Recovery Mode using Command + Option + R to attempt to access the most recent online macOS installer that is compatible with your Mac. Unfortunately some Macs may only boot to the online installer for the OS which originally shipped with the computer from the factory. The original factory OS will not recognize the new drive layout or APFS file system utilized by more recent versions of macOS.

If you are booting into a later macOS installer such as Big Sur, Monterey, Ventura, or Sonoma and you don't see the physical internal drive or volume, then the drive has most likely failed. Within Disk Utility click "View" and select "Show All Devices" so that the physical drive and hidden APFS Container appears on the left pane of Disk Utility (this option is not available with older versions of macOS).

Hey there!

What is the year and model of your iMac? If your Mac is older, you can use an external solid state drive (SSD) as your new startup disk if the internal one has failed.

-Jack