Samsung
Turn Notifications On or Off for Individual Apps auf Samsung
By default, every app installed on a Samsung phone is allowed to push notifications to your lock screen, status bar and notification panel. Once you install an app like WhatsApp, a game or a shopping app, it usually asks for notification permission right away and keeps sending alerts until you change that setting yourself.
Samsung manages these permissions individually, so muting one chatty app never touches alerts from anything else on your phone. Open Settings ➔ Apps ➔ select the app ➔ Notifications, then switch Show notifications off to block all alerts from that app, or back on to restore them.
Many apps break their notifications down further once you reach this screen. WhatsApp, for example, lets you keep notifications for direct messages active while turning off alerts for group chats specifically, so you don't have to silence the whole app just to escape one noisy group.
Turning off notifications completely means you won't see anything from that app, not even a silent entry in the panel, until you switch it back on. If you only need quiet hours instead of a permanent block, a scheduled Do Not Disturb mode is usually the better fix, since it mutes everything temporarily without changing any individual app permission.