clean and wipe your i Mac computer
I Mac retina 5k 27 inch late 2015 Mac Big Sur do not wish to update to motaray
just wish to do a clean and wipe of I Mac computer
Mac Pro, OS X 10.11
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If you want to erase your iMac, follow the steps in the second part of this article:
What to do before you sell, give away, trade in, or recycle your Mac - Apple Support
After that you can also start up in Recovery Mode and get the last used macOS reinstalled automatically: