const q = vscode.window.createQuickPick();
q.items = [{ label: "1" }, { label: "2" }];
q.activeItems = [{ label: "2" }];
q.show();

Based on my understand of vscode extension api doc.

/**
  * Active items. This can be read and updated by the extension.
  */
activeItems: readonly T[];

it should active "2" item when quickpick is showing. But I found activeItems will reset after show() method; I dont know why and cant find any same issue in the internet,