Sadly it appears not to be that simple.
I just measured the “Liquid Retina XDR Display” of my 14" M2 MacBook Pro in a couple of the out-of-the-box preset profiles.
Using the default Apple XDR Display (P3-1600 nits) profile, the EOTF is indeed a close match to a pure 2.2 power curve for an Apple Display P3 tagged buffer.
However when set to the HDR Video (P3-ST 2084) profile, it appears that an Apple Display P3 tagged buffer is converted to ST.2084 using the piecewise sRGB curve.
So the HDR “reference mode” acts like a PQ display emulating the piecewise sRGB EOTF, but in “normal” mode it matches the behaviour of older Apple displays, where an image with an sRGB profile has its pixel values left “as is” and sent to a display with a pure 2.2 exponent EOTF.
MBP14_XDR_Display_plots.pdf (38.9 KB)