When you are previewing high contrast themes and using the down and up arrow to see them. The High Contrast selections are not highlighted.
Example:

(Experimental duplicate detection)
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Looks like the quick picker doesn't render the high contrast selection border
Is there a way to solve this?
I tried manny settings like "menu.selectionBackground", "selection.background", "list.activeSelectionBackground", "editor.selectionBackground": "#758df7", "terminal.selectionBackground" but none of them worked.
Most helpful comment
Looks like the quick picker doesn't render the high contrast selection border