I have managed to do most of the window, but I am really struggling with the arch, I have tried the spin tool, but it can't quite manage the pointiness of the three arches.
2 Answers
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You can try with CtrlE (or header menu > Edge) > Bridge Edge Loops, then you'll need to tweak the values in the Operator box (especially Number of Cuts and Smoothness) and probably edit a bit so that it matches your precise shape:
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Using Proportional editing > Root should get you pretty close.
Use more vertices on the sides for smoother result ;)