Opencore and Windows dualboot.

I have a [40gb USB2.0] external disk and 500gb[SATA] internal disk.

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So can i install windows on 500gb[SATA] disk and macOS HighSierra 10.15.3 [Opencore] on 40 gb [USB2.0] drive and dualboot.

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I tried it once before but realised couldnt do it on a single disk with partition and windows installed and ended up not able to boot into windows :'( . Fortunately i had a backup so no data was lost, but had to do a fresh install.

So do i have to start fresh and reinstall windows to do this dualboot? And is it actually possible with a partition on a single disk?

I have the OpenCore recovery bootable i made in the last try

Please help.

Thank you!