Which restriction is unique to the background layer in design software?

The restriction that is unique to the background layer in design software is that it cannot be locked. Typically, a background layer is often the base layer in a file, and it usually has specific properties that differentiate it from other layers.

When a layer is designated as a background, it is automatically placed in a locked state, preventing manipulation such as resizing or moving without converting it to a standard layer first. This feature serves to maintain the integrity of the initial design foundation. Although various layers can be locked to prevent accidental edits, the background layer starts in a locked state by default and lacks the flexibility of being freely locked or unlocked.

This characteristic influences how designers approach their projects, encouraging them to convert the background layer to a regular layer if they need it to be editable, including the ability to apply blending modes and other adjustments.