Function render_popover 

pub fn render_popover(
    view: &ViewHandle,
    win_w: u32,
    win_h: u32,
    w: u32,
    h: u32,
) -> Rendered

Present view in a real window and capture the popover it puts up.

A .popover is not an attached sheet — it gets its own _NSPopoverWindow, which is why render_sheet cannot see it. This finds that window among the application’s and captures it.

Returns a single flat pixel if no popover appeared.