I have tried the “Glare” node on a light-emitting sphere, and the first image is what I got. the second image is a screen capture of a YouTube video for “camera flash”. The first image looks like a fake. Can I get a more realistic camera flash in Blender?
One way to improve is to chain glare nodes, use 2 or 3 with different strength, angles and count of streaks.
Or mix it with an real photo flash prepared in a paint programm.