Can't find any guides for multibooting opencore and windows 10 on a one SSD on with windows 10 already installed

Hello guys, I was following the Dortania guide on how to dual boot macOS big sur and windows 10 on same drive (I have a laptop so I can't add another drive) and I already have windows 10 installed, but unfortunately the tutorial on how to do so isn't finished yet, and I already searched a lot for a solution on google but I can't find anyone who installs macOS without formatting windows, so any suggestions?

submitted by /u/DesignMASTERed
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