activate_HDR.applescript

use AppleScript version "2.4" -- Yosemite (10.10) or later
use framework "Foundation"
use framework "AppKit"
use scripting additions

tell application "System Settings"
	activate
	current application's NSWorkspace's sharedWorkspace()'s openURL:(current application's NSURL's URLWithString:"x-apple.systempreferences:com.apple.Displays-Settings.extension")
	delay 0.5
	
	tell application "System Events"
		tell process "System Settings"
			key code 48
			key code 48
			key code 48
			key code 123
			delay 0.5
			-- activate hdr on left monitor
			
			set hdr to checkbox 1 of group 3 of scroll area 2 of group 1 of group 2 of splitter group 1 of group 1 of window "Displays" of application process "System Settings" of application "System Events"
			tell hdr
				if value is 0 then click it
			end tell
			
			-- switch to right monitor by key navigation. Actions like "click" are not invocable on the buttons.
			-- hit "tab" (key code 48) three times, it's the only way to be sure ;-)
			
			-- hit "right" to select the right monitor
			key code 124
			delay 0.5
      
      			-- do it again
			set hdr to checkbox 1 of group 3 of scroll area 2 of group 1 of group 2 of splitter group 1 of group 1 of window "Displays" of application process "System Settings" of application "System Events"
			tell hdr
				if value is 0 then click it
			end tell
			
		end tell
	end tell
	quit
end tell

@skempken it works perfectly, do you mind sharing the code so that I can just save my UUID into the program and compile it?

See this PR alin23/mac-utils#5