Back in the day, if you did the combination of command-option-shift click while in the curves adjustment window, it would mark those points on all channels so you could then make adjustments to that one place. That seems to be gone. Is it? Is there a replacement? That click/drag curve point is not what I'm needing.
Open Curves panel.
Activate Targeted Adjustment Tool (the little finger thingy).
Command-click on image places a point on the active curve.
Shift-command-click places points on the all of the color channel curves.
Cycle through channels:
Option-2 for composite channel
Option-3, 4, 5, 6 (if CMYK) for individual color channels.
Takes a while to get used to, but it's the reality now. You'll get used to it.