::Likely, what’s happened is the “Square” game object’s Sorting Layer is above the “Particle System”.
Simply go to either the Square’s Sprite Renderer and set the Order in Layer to [-1],
Or go to your Particle System’s Particle System > Renderer > Order in Layer to [1] or change Sorting Layer ID to Background/Midground/Foreground.
If you encounter a similar issue like this, I would recommend checking for any blocking sprites by setting your other in scene objects to inactive, and checking if you can see your desired sprite. (if you know that the blocked sprite is normally visible and working).
.
