The question I saw most this year (2021) was “what are the black spots on the back of cicadas for”? The people asking this question are specifically talking about Magicicada cicadas that have recently molted and are still white/cream colored and soft (teneral from the Latin word “tenen” meaning soft).
The area of the cicada where the black spots appear is called the pronotum — “pro”, meaning before in Greek, and “notum”, meaning the back, also in Greek. Before the back.
The spots contain a pigment that will gradually spread throughout a cicada body as it hardens, and transforms from white to black.
People speculate that the two black spots resemble eyes, and that might scare away predators. This might be possible, but I haven’t read anything to substantiate the hypothesis.