Hi @lilrizzy
Seems as though the display has been internally damaged.
The display will have to be replaced as it cannot be repaired.
Here's a [https://www.youtube.com/watch?v=hqsuSiZrbgc|video] that shows what to do.
Search online for ''Galaxy A21s SM-217F LCD display + touch screen digitzer'' to find suppliers that suit you best.
If doing this yourself is too daunting, contact a reputable, professional mobile phone repair service and ask for a quote to replace the screen