WhatsApp for Samsung Galaxy S9

This is almost always the proximity sensor, the screen blanks when it thinks the phone is near your face but stays black if the sensor is blocked by a thick case, a screen protector, or dirt over the top of the display near the earpiece. Wipe that area clean and remove any film covering it. You can check the sensor by dialing *#0*# to open the hardware diagnostics menu and running the Sensor test. If the screen still won't wake during calls, force-stop WhatsApp under Settings > Apps > WhatsApp > Force stop and clear its cache under Storage. See how others solved this on Reddit

Open WhatsApp > tap the three dots > Settings > Storage and data > Media auto-download, and turn off auto-download for photos, audio, video and documents on mobile data so the app downloads less in the background. Then in One UI go to Settings > Apps > WhatsApp > Battery and choose Restricted for the biggest saving (Optimized is only the default). Note that Restricted, or letting Android put WhatsApp into the Deep sleeping list under Settings > Battery and device care > Battery > Background usage limits, can delay your notifications, so if you rely on instant alerts use Optimized instead and keep WhatsApp out of the sleeping lists. See how others solved this on Reddit

WhatsApp can hide downloaded media from your Gallery, so the files exist but the Gallery's media scanner skips the folder. Open WhatsApp > Settings > Chats and turn on Media visibility, and for a specific conversation open the contact/group info and set Media visibility to Yes there too. If photos still don't appear, go to One UI Settings > Apps > WhatsApp > Permissions and confirm the Files/Storage permission is allowed, then restart the phone so the media scanner re-indexes the WhatsApp Images folder. See how others solved this on Reddit

WhatsApp on Android backs up to Google Drive, so first make sure the old phone backed up via WhatsApp > Settings > Chats > Chat backup using the Google account you'll use again. Then install WhatsApp on the S9, sign in with the same phone number, and tap Restore when prompted during setup. The restore prompt only appears on a fresh install before you finish verifying, and it works only if both the phone number and Google account match. If your old chats were on an iPhone, iCloud and Google Drive backups aren't cross-compatible, so you'd need an official or paid transfer tool. See how others solved this on Reddit

Yes. You can register WhatsApp on a Wi-Fi-only device, but verification still needs a phone number you control to receive the one-time code, choose the Call me option if an SMS can't reach the tablet. After it's verified, WhatsApp runs fine over Wi-Fi alone. Alternatively, instead of registering a separate account, link the tablet to your main phone: on the phone open WhatsApp > Settings > Linked devices > Link a device and scan the QR code shown on the tablet. The linked-device method keeps all your existing chats in sync without a second registration. See how others solved this on Reddit