Slow motion flickering

Hey Waseempasha21,

If you haven't already, restart your iPhone then try the slow motion feature again with your video. Restarting can resolve many odd issues: Restart your iPhone - Apple Support

If the behavior continues, do you use a case with your iPhone? If so, remove it to see if that helps as some case material can cause interference as shown here: If the camera or flash on your iPhone, iPad, or iPod touch isn't working - Apple Support

Keep us posted.

Take care!

This problem occurs because of external camera protectors or guards which restrict the camera to deliver to its full potential.

Thank You