Plutonium

As long as you have Discord Rich Presence enabled, you should be able to click the button to upload something on Discord and then click Game Invite. I'm at work so I can't check exactly how it works right now but that should do the trick.

@Koby_tko well it should display an error message that tells him why. Maybe he's trying to use special characters in his username?

same as the vanilla game, but you need windows 8.1/10 and a GPU that supports DX 11 on a hardware level. https://www.systemrequirementslab.com/cyri/requirements/call-of-duty-modern-warfare-3/11232