What causes the P0191 code on the L5P, and how much is it going to cost me?

[OilSlickSam]

My 2019 just threw a P0191 (Fuel Rail Pressure Sensor) code and went into reduced power mode. What is the deal with these sensors? I’ve heard they are a nightmare to get to because they are buried under the intake. How is everyone handling this—are you letting the dealer do it under warranty or is it a DIY job?