WhatsApp for Samsung Galaxy S21 Ultra

One UI's aggressive battery optimization is suspending WhatsApp when the screen is off, which delays notifications until you reopen the app. Go to Settings > Apps > WhatsApp > Battery and set it to Unrestricted, then open Settings > Battery and device care > Battery > Background usage limits and make sure WhatsApp is removed from the 'Sleeping apps' and 'Deep sleeping apps' lists. Also turn off Settings > Battery and device care > Auto optimize daily if it keeps re-adding the app. See how others solved this on Reddit

This is usually a corrupted cache or a stale app version after a system update. First clear the cache via Settings > Apps > WhatsApp > Storage > Clear cache (this keeps your chats), then update WhatsApp from the Play Store. If freezing continues, also exempt WhatsApp from battery restrictions under Settings > Apps > WhatsApp > Battery > Unrestricted, and reboot the phone. See how others solved this on Reddit

After a One UI update, WhatsApp's storage permission can revert and media downloads silently fail. Go to Settings > Apps > WhatsApp > Permissions and grant 'Files and media' (allow management of all files), then confirm your phone still has free internal storage. Make sure WhatsApp isn't restricted from data: under Settings > Apps > WhatsApp > Mobile data, enable both 'Allow background data usage' and 'Allow data usage while Data saver is on'. Finally, inside WhatsApp open Settings > Storage and data > Media auto-download and re-enable downloads for Wi-Fi and mobile data, then restart the phone. See how others solved this on Reddit

WhatsApp heavily compresses images by default, which is very visible on the S21 Ultra's high-resolution camera. In a chat, tap the attach (paperclip) icon, choose your photo, then tap the 'HD' icon at the top and select 'HD quality' before sending. For maximum quality on important shots, send the picture as a document via attach > Document instead, which skips compression entirely. See how others solved this on Reddit

WhatsApp video calls cap resolution based on connection stability, and a data saver can throttle it further. In WhatsApp, open Settings > Storage and data and turn off 'Use less data for calls'. Then disable the system data saver for WhatsApp under Settings > Connections > Data usage > Data saver. A strong 5GHz Wi-Fi or solid 5G signal makes the biggest difference, since the app drops resolution the moment it detects packet loss. See how others solved this on Reddit

When a Bluetooth headset is connected, the S21 routes the mic to the headset, and if its mic profile glitches the voice note records silence or stops early. As a workaround, briefly disconnect Bluetooth so it records through the phone's built-in mic, or hold the device to your mouth while recording. Clearing the WhatsApp cache (Settings > Apps > WhatsApp > Storage > Clear cache) and re-pairing the headphones under Settings > Connections > Bluetooth also resolves the routing bug for many users. See how others solved this on Reddit