The display panel has gone haywire. Sometimes it will fuzz out, or get brighter and brighter until it's all white. Most of the time it never comes on.
There have been issues where the second generation Toyota Prius displays have failed over time. The solder joints where the vehicle wiring harness connects to the display can vibrate and break over time, leading to connection issues and malfunctions. Sometimes these displays can be repaired by an electronics technician familiar with the construction of the Prius displays. Most of the time the display will need to be replaced. You may want to enlist the help of a mechanic, such as one from YourMechanic, who can diagnose your electrical system and recommend a proper course of repair.
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