Me and 2 of my friends recently did a speed run in dead rails and it was rejected because my friends didnt have a pov and the video didnt have sound.

Q1: M 2 friends are in mobile and im in PC if we do this run again should i submit it as PC or mobile?

Q2: We dont want our personal voices or background voices in the video can we submit it with just the game sound?

Q1: M 2 friends are in mobile and im in PC if we do this run again should i submit it as PC or mobile?

I would set the platform to whatever player 1 or who submits the run is playing on.

For the other player, I would write in the description what platform they were on. Also, there isn't really a mobile platform, so you would say Android or iOS.

Q2: We dont want our personal voices or background voices in the video can we submit it with just the game sound?

Yes, that is fine. If anything your voices could stop people from hearing the game's audio. And Deal Rails' rules only requires in-game audio.