Why is React complaining about missing keys in a normal JSX chunk?

Question

React

React throws an error: "Warning: Each child in a list should have a unique "key" prop" on a normal piece of JSX. Don't tell me why?

There is a component:

{
        data.map((element) =>
          <Card
            key={element.key}
            img={element.img}
            name={element.name}
            handleToggle={element.action()}
            hoverTitle={element.hoverTitle}
            desk={element.desk}
            btnText={element.btnText}
            btmMod={element.btmMod}
            imgMod={element.imgMod}
            bgMod={element.bgMod}
          />
        )
      }

Card Component:

spoiler

<div
      className={"card " + (bgMod)}
      ref={cardWrapper}
    >
      <div
        className={"card__nav card--zIndex"}
        onClick={() => handleToggle(cardWrapper)}
      >
        <svg></svg>
      </div>
      <div className={"card__img " + (imgMod)}>
        <img alt={name} src={img} />
      </div>
      <div className={"card__name card--zIndex"}>
        {name}
      </div>
      <div className={"card__desk"}>
        {desk}
      </div>
      <div className={"card__hover-title"}>
        {hoverTitle}
      </div>
      <Button
        mod={btmMod}
        text={btnText}
      />
        <svg></svg>
      <div className={"card__inner"} />
    </div>

If you remove {hoverTitle} in the Card component, the error will disappear. Do not tell me how to fix this and why this error appears? After all, I always thought that it was only necessary to specify keys when generating elements, but this is clearly not the case here.