S21 ULTRA Fingerprint scanner issue.

Thank you for contacting Samsung KSA

Please ensure specific tips for better fingerprint recognition:

Your device has a built-in fingerprint recognition sensor at the bottom center of the screen. Ensure that the screen protector or the touchscreen on the fingerprint recognition sensor area is not scratched or damaged by objects

If protective film/screen protector is dirty or scratched, please replace to new one and we recommend to register your fingerprint again for better fingerprint recognition rate after replacing protective film. 

Ensure that the fingerprint recognition sensor area at the bottom center of the screen and your fingers are clean and dry

 If you bend your finger or use a fingertip, the device may not recognize your fingerprints. Press the screen so that your fingertip spreads over the wide surface of the fingerprint recognition area. 

 The device may not recognize fingerprints when attaching screen protective film or screen protector unapproved by Samsung

We recommend to use only Samsung-approved accessories and you can purchase Samsung-Approved protective film from your local Samsung retailer or Authorized Samsung Service Center.

In case that you try to recognize fingerprints from too dry fingers, the device with ultrasonic fingerprint sensor may not recognize fingerprints and recognition rate may be also low. If the recognition rate is low, device tries scanning repeatedly to get the fingerprints with better quality so unlocking speed by fingerprint may become slowly. However this is not a device defect but normal operation.
If you let your finger be moist properly by using hand cream and try again, the recognition speed will be better.

and if you still face the same issue try to perform interactive check through Samsung Members app (get help page-interactive check-finger print)

We hope this has been of some assistance to you. If you do have any further queries, please do not hesitate to contact us.

Hope you and your family staying healthy and safe!