GTA 5 on 2 different devices at the same time?

I wanted to know if you can now play GTA 5 on two devices at the same time with the same account (I have a gaming PC and a Steam deck).

Wanted to play with my friend (he on the Steam deck and I on the PC) but with the same account.

Is that possible?

Because you can create lots of different characters, I wanted to ask if you can create two characters and one plays on one and the other on the other, but with the same account.

Is it possible on Steam to have an account on two devices and both play the same game at the same time or different games at the same time?