How do I install MacOS Venture using OCLP and Win 10 with WintoUSB on an SSD Ext HHD?

[Clever_fox]

I have late 2013 27 inch imac that I love!! But I do not want to open it to put faster drives in it. I bought a 1 TB SSD Ext HD. I can install Ventura or Win 10 on the SSD fine, but not together on the same drive. I have searched the web and I can not find steps to do the install. When I try installing both each process OCLP and WintoUSB they want to format the whole drive. The process formats the whole drive blowing away whatever OS I install first. It does not matter how I partition them, or I am doing it wrong. I am trying to use UEFI with both OSs'. If anyone can help it would be great. I just got it this past xmas for a good price on ebay and it is a beast and a half.