Magento Notification Bar enables an alert bar in frontend to engage visitors with offers, news, discounts, social media buttons, etc.
The Magento Top Notification Bar extension is what you need for flash sales, offering discounts, request the visitors for the subscription to your newsletters and the countdown timer for periodic offers.
Learn the stepwise configuration of the Magento Notification Bar extension at https://meetanshi.com/blog/magento-notification-bar/