WhatsApp for Samsung Galaxy S10

On Samsung phones this is usually caused by One UI's aggressive power management putting WhatsApp to sleep in the background. Open Settings > Apps > WhatsApp > Battery and set it to Unrestricted, then go to Settings > Battery and device care > Battery > Background usage limits and remove WhatsApp from both the Sleeping and Deep sleeping apps lists. If it still feels sluggish, clear the cache (not data) via Settings > Apps > WhatsApp > Storage > Clear cache, which won't delete your chats. See how others solved this on Reddit

Delayed notifications on the S10 almost always come from One UI putting WhatsApp into deep sleep so it stops checking for messages. Open Settings > Battery and device care > Battery > Background usage limits and remove WhatsApp from the Sleeping and Deep sleeping apps lists, then set Settings > Apps > WhatsApp > Battery to Unrestricted. Finally confirm notifications are enabled both inside WhatsApp (Settings > Notifications) and in the system settings (Settings > Apps > WhatsApp > Notifications). See how others solved this on Reddit

This is usually a broken or muted notification channel. Go to Settings > Apps > WhatsApp > Notifications, open the Message notifications category, and re-select a Sound, making sure importance is set so it 'Makes sound' (Alert) rather than Silent. Also check that Do Not Disturb isn't active (Settings > Notifications > Do not disturb). If it still won't sound, clear the WhatsApp cache via Settings > Apps > WhatsApp > Storage, then toggle the notification channel off and back on to rebuild it. See how others solved this on Reddit

To make the screen turn on for messages, the notification channel must be set to alert with a pop-up, not run silently. Open Settings > Apps > WhatsApp > Notifications, tap the Message notifications category, set it to 'Alerting' / make sound, and enable 'Pop-up'. Then in Settings > Notifications, make sure pop-up style is set to Detailed (not Brief, which is less likely to wake the screen). Low-importance or silent channels never wake the display, so fixing the channel level is the key step. See how others solved this on Reddit

For a heads-up banner you need the channel set to alert with pop-up enabled. Go to Settings > Apps > WhatsApp > Notifications > Message notifications, set importance to 'Alerting' (makes sound and pops on screen), and turn on 'Pop-up'. In Settings > Notifications set the pop-up notification style to Detailed so the banner shows content. Keeping WhatsApp out of the Sleeping/Deep sleeping lists (Settings > Battery and device care > Background usage limits) ensures these banners arrive in real time. See how others solved this on Reddit

After a One UI update the custom sound for WhatsApp's channel can reset to Silent or None. Reopen Settings > Apps > WhatsApp > Notifications > Message notifications > Sound and pick a tone again, and confirm Do Not Disturb isn't on (Settings > Notifications > Do not disturb). If the sound still won't apply, clear the WhatsApp cache in Settings > Apps > WhatsApp > Storage, and as a last resort reinstall WhatsApp from the Play Store so the notification channels are recreated cleanly. See how others solved this on Reddit