Display disconnecting after trauma

Unless you've actually opened up the screen and verified that there's a problem with the motherboard connector, that is rarely the cause for screen problems, especially after a drop. Virtually every smartphone out there locks down all of the internal connectors with screws and brackets of some sort, so even a hard fall won't dislodge a connector.

Far more common is that a fall damages or knocks loose the delicate connection between the flex cable and the glass the display circuitry is printed on, and that kind of damage isn't repairable. On your phone we know it's not a backlight problem since you don't have one, so the recommended repair in your case is almost certainly to replace the screen. iFixit sells the screen+battery assembly but not the screen by itself, although they have repair guides for both cases. Assuming you don't need a new battery, here's the screen only replacement guide.

Samsung Galaxy S21 Screen Replacement - iFixit Repair Guide

For a replacement screen, you can start with the big three, Amazon, eBay and AliExpress, but a general internet search using your phone's model number is sure to turn up other choices as well.

Note that most sellers will allow you to plug the screen in before installing it to verify that replacement will fix the problem; in case it doesn't they will usually accept a return.

Good luck and let us know how it goes.