You CAN´T boot or install a legacy windows installation from OCLP boot picker, always will give you errors.
I may be misunderstanding what you mean by "legacy windows installation" but this is empirically not true here
on a rMBP 2012 and using the Dortania link works if you follow it to a tee, and if you do not follow it exactly, I have seen the kinds of errors with aborted boots that pepepro appears to be seeing.
If you mean something else ignore this post. Ah well. If another way works for someone else then great.
I am in no way a WinGuru.
the only thing i changed was the creation of the usb stick - i did it on another windows machine with the help of rufus, to overcome windows 11's hardware restrictions right from the beginning.
FWIW, I believe that may be the issue here. Using regedit as described in the Dortania link
to a tee (I have seen the kinds of errors with aborted boots that you appear to be seeing when skipping or missing steps in that instruction )
has worked here, including the three simple regedit "live" edits during the install at the "This PC can't run Windows 11." dialog.
Ah well. Good luck regardless of your strategy.