Is a player considered a publisher of a war game that contains Sharia prohibitions if the game automatically portrays gameplay from each player's perspective? Is he sinful for playing it? Is he sinful if other players publish video clips of the gameplay with music? And what is the ruling on playing with someone who uses a plane with a cross on it?

You must repent to Allah Almighty for playing a game that includes শরিয়া prohibitions. The conditions for repentance are: refraining from the sin, regretting it, and resolving not to return to it, along with seeking forgiveness. Do not despair of Allah's mercy, for Allah forgives all sins. The sin of creating the game falls on its creator. This type of question is closer to waswasah (whispers of Satan/obsessive thoughts), so you should disregard it. Minimize your engagement with games in general, even permissible ones, and utilize your time for what benefits you in matters of your religion and your worldly life. Do not give in to waswasah and doubts, as their consequences are severe. Ibn Hajar al-Haytami says that the cure for waswasah is to completely disregard it.