Пример:

import authForm from './modals/authform';
import {useEffect, useState} from "react";

export default function Header(props) {

    const [showAuth, setShowAuth] = useState();

    return (
        <authForm showAuth={showAuth} setShowAuth={setShowAuth}/>
    );

}

Ошибка:

React does not recognize the `showAuth` prop on a DOM element. If you intentionally want it to appear in the DOM as a custom attribute, spell it as lowercase `showauth` instead. If you accidentally passed it from a parent component, remove it from the DOM element.

Решение:

Изменить регистр при импорте компонента authForm на Authform. Дело в том, что react неверно воспринимает camelCase в качестве компонента.

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