On the graph, the black line is the preferred target frequency response for speakers, and the blue line is for headphones. In both cases, we see a rise in low frequencies and a decline in high frequencies.
But judging by the graph, it's not a linear frequency response, is it? Everything is right. This is a preferred curve, taking into account the lack of emulation of space and reflections in headphones. In fact, the researchers found such equalization settings to compensate for the absence of a room when listening with headphones.
If you use dSONIQ Realphones and apply binaural emulation of reflections and crossfeed signals (crossfeed) to the aligned frequency response of headphones, then you do not need to use the Harman curve.
Many manufacturers have released models customized for this curve. From full-size headphones, these are: AKG N700 NC, K361, and K371, and in-ear headphones: JBL Live 200, 500, and 650, Samsung Galaxy Buds, JBL Reflect Flow, Truthear x Crinacle ZERO.