patch-edid.rb

#!/usr/bin/ruby
# Create display override file to force Mac OS X to use RGB mode for Display
# see http://embdev.net/topic/284710

require 'base64'

data=`ioreg -l -d0 -w 0 -r -c AppleDisplay`

edids=data.scan(/IODisplayEDID.*?<([a-z0-9]+)>/i).flatten
vendorids=data.scan(/DisplayVendorID.*?([0-9]+)/i).flatten
productids=data.scan(/DisplayProductID.*?([0-9]+)/i).flatten

displays = []
edids.each_with_index do |edid, i|
    disp = { "edid_hex"=>edid, "vendorid"=>vendorids[i].to_i, "productid"=>productids[i].to_i }
    displays.push(disp)
end

# Process all displays
if displays.length > 1
    puts "Found %d displays!  You should only install the override file for the one which" % displays.length
    puts "is giving you problems.","\n"
elsif displays.length == 0
    puts "No display data found!  Are any external displays connected?"
    puts "\nNote: Apple Silicon (arm64) devices are currently unsupported, as the standard"
    puts "method of retrieving display information does not work."
end
displays.each do |disp|
    # Retrieve monitor model from EDID display descriptor
    i = disp["edid_hex"].index('000000fc00')
    if i.nil?
        monitor_name = "Display"
    else
        # The monitor name is stored in (up to) 13 bytes of text following 00 00 00 fc 00.
        # If the name is shorter than 13 bytes, it is terminated with a newline (0a) and then padded with spaces.
        monitor_name = [disp["edid_hex"][i + 10, 26].to_s].pack("H*")
        monitor_name.rstrip!            # remove trailing newline/spaces
    end

    puts "Found display '#{monitor_name}': vendor ID=#{disp["vendorid"]} (0x%x), product ID=#{disp["productid"]} (0x%x)" %
            [disp["vendorid"], disp["productid"]]
    puts "Raw EDID data:\n#{disp["edid_hex"]}"

    bytes=disp["edid_hex"].scan(/../).map{|x|Integer("0x#{x}")}.flatten

    puts "Setting color support to RGB 4:4:4 only"
    bytes[24] &= ~(0b11000)

    puts "Number of extension blocks: #{bytes[126]}"
    puts "removing extension block"
    bytes = bytes[0..127]
    bytes[126] = 0

    bytes[127] = (0x100-(bytes[0..126].reduce(:+) % 256)) % 256
    puts
    puts "Recalculated checksum: 0x%x" % bytes[127]
    puts "new EDID:\n#{bytes.map{|b|"%02X"%b}.join}"

    Dir.mkdir("DisplayVendorID-%x" % disp["vendorid"]) rescue nil
    filename = "DisplayVendorID-%x/DisplayProductID-%x" % [disp["vendorid"], disp["productid"]]
    puts "Output file: #{Dir.pwd}/#{filename}"
    f = File.open(filename, 'w')
    f.write '<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">'
    f.write "
<dict>
  <key>DisplayProductName</key>
  <string>#{monitor_name} - forced RGB mode (EDID override)</string>
  <key>IODisplayEDID</key>
  <data>#{Base64.encode64(bytes.pack('C*'))}</data>
  <key>DisplayVendorID</key>
  <integer>#{disp["vendorid"]}</integer>
  <key>DisplayProductID</key>
  <integer>#{disp["productid"]}</integer>
</dict>
</plist>"
    f.close
    puts "\n"
end             # displays.each

Based on the current situation, TVs still switch back to YCbCr color in HDR mode, such as LG's C series and G series TVs.

Is it possible to support using RGB in HDR mode as well?

@LeXwDeX Most of the time, TVs will default to YCbCr 4:2:2 whenever you enable HDR, especially if your Mac's HDMI port is version 2.0.

It's usually limited by the bandwidth of the HDMI port and the formats (HDR10, HLG, Dolby Vision) announced during the handshake.

You can check with USB-C/Thunderbolt-to-HDMI adapters to work around this if you really want to, but usually it will just not work reliably or introduce other issues