Haven’t those been phased out at most major airports? I fly with some frequency and all the TSA agent sees is an illustration of my body shape. Apparently this is using milimetre waves
The machine creates a detailed pornographic-detail-grade image [1]. You have no way to know if it is saved. What is displayed on the external screen is not relevant.
[1] https://www.researchgate.net/figure/Image-generated-by-L3-mi...