Here's a mod for split screen!

[bullettrain101]

https://github.com/ZeroFox5866/nucleuscoop/releases

This mod let's you play with a total of 16 people depending on how strong your PC is. All campaigns, multiplayer's and firefights are playable with their respective player cap (possible mods to change that), but AFAIK you can't do any online modes. Also, I believe it works with cross play via LAN (Split screen works via LAN here)

Have fun!

[Cool Cereal]

Thanks for the reminder of this mod's existence!