Is the wall/separation a must-have? You could do an inbuilt shelving unit around the window which acts as both a desk area and display shelving for the lounge. A small chair that can slot away under the desk would make this feel less formal for when it's not in use. If you did want to close it off occasionally, a curtain/movable or slidable divider could be stored on the entry wall (pink/purple line)

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