We are sorry to hear about your experience with your Samsung Galaxy Z Flip 4 having issues with dead pixels on the screen, and we apologize for the inconvenience it caused you. If it happens to my device, I'll get worried too.
Similar to our dear Samsung members' replies, I recommend bringing your device to the nearest Samsung Service Center in your area.
Rest assured that our Samsung engineers and technicians are competent to assess your device, offer suggestions, and provide prompt solutions to restore it to optimum performance.
For more assistance and guidance, you may contact us via our online Samsung Customer Care support channels below.