could you clarify what you mean by a 'minimized notification'? Notifications are either showing or not showing, with a possibility to expand some if you want some more detail (depends on the app), but if you don't swipe it away there isn't an opportunity to get another notification sound.
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Welcome to Android Central! Go to Settings>Apps, select the app whose notifications have become Silent, and select the notification channel in question. Change it from Silent to Default.