This is the first Mod or Hack that allows 20 Civs / players in MP

[midn8t]

You need to change Edit File called StagingRoom.lua

located Steam\steamapps\common\Sid Meier's Civilization VI\Base\Assets\UI\FrontEnd\Multiplayer

The first thing you may want to do is remove the warring for unsupported number of players

look for this line
-------------------------

end
-- This is weird sauce, it probably should be something better later
if playerID > 7 then
statusString = statusString .. "[NEWLINE][COLOR_Red]" .. UnsupportedText;
if statusTTString ~= "" then
statusTTString = statusTTString .. "[NEWLINE][COLOR_Red]" .. UnsupportedTextTT;
else
statusTTString = "[COLOR_Red]" .. UnsupportedTextTT;
end
end

-----------------------
Change it to this
-----------------------

end
-- This is weird sauce, it probably should be something better later
if playerID > 20 then
statusString = statusString .. "[NEWLINE][COLOR_Red]" .. UnsupportedText;
if statusTTString ~= "" then
statusTTString = statusTTString .. "[NEWLINE][COLOR_Red]" .. UnsupportedTextTT;
else
statusTTString = "[COLOR_Red]" .. UnsupportedTextTT;
end
end

-------------------

that will remove the red warning

next part

everything that has to do with anything when comes to limiting number of players in MP has to do with this g_currentMaxPlayers

there is line in file and I have mine set to this
------------------------

local g_currentMaxPlayers = math.min(MapConfiguration.GetMaxMajorPlayers(20), 20);

-------------------------

just changing the ,12) to 20 does not help you need put the both 20s in there or at least I did (20), 20);

then there is one more line you need to change and that is below

----------------------------------------------------------------
-- Event Handlers
----------------------------------------------------------------
function OnMapMaxMajorPlayersChanged(newMaxPlayers : number)
if(g_currentMaxPlayers ~= newMaxPlayers) then
g_currentMaxPlayers = math.min(newMaxPlayers, 12);
if(ContextPtr:IsHidden() == false) then
CheckGameAutoStart(); -- game start can change based on the new max players.
BuildPlayerList(); -- rebuild player list because several player slots will have changed.
end
end
end


Change that to

----------------------------------------------------------------
-- Event Handlers
----------------------------------------------------------------
function OnMapMaxMajorPlayersChanged(newMaxPlayers : number)
if(g_currentMaxPlayers ~= newMaxPlayers) then
g_currentMaxPlayers = math.min(newMaxPlayers, 20);
if(ContextPtr:IsHidden() == false) then
CheckGameAutoStart(); -- game start can change based on the new max players.
BuildPlayerList(); -- rebuild player list because several player slots will have changed.
end
end
end


I have not figured out how to fix add button to appear at bottom of list it appears in middle and will add down list but you should see all 20 spots ether way and it will start a game with 20 total in game as MP


after that you can or should also change the mapsize.xml file the Mapsize file replaces the gameinfo file settings in civ4 and civ5 for mapsizes aka name

in there is all map sizes with default number of players allowed this file may also need be changed but changing map file by it self does nothing for MP but will work for hot seat