Is the other Magnus supposed to be straight edge?

First of all, being straight edge is way more than just not taking drugs. It's also not inflicting pain to another living being (that means a lot of straight edge are vegans,) not drinking alcohol, not smoking (even cigarettes,) and not having sex without feelings. There is a whole variety of types of music, including punk in general but mostly its subgenre, hardcore.

Considering that the series is German, we can assume that the creators did know what this symbol meant. According to the German Wikipedia page of Straight Edge, the community represents between 11,000 and 17,400 people in Germany.

Now, with all this information, to confirm that Magnus is indeed straight edge would be to check if any of the flyers on the wall are related to music bands that are themselves straight edge. I don't have the while season in mind, so I can't remember if he drinks alcohol or eats meat. I will check later on and edit my answer then.

Even if he does drink alcohol, the fact that he has an X tattooed on his hands is a statement strong enough to affirm that he is. He also has a strong position against drugs, which is the principal position of being straight edge.

The fact that he gets angry at his father is more that his father doesn't pay attention to him at all and doesn't even know what the positions of his son are, even though his son has it tattooed all over his body.

Even if Magnus has it tattooed all over his body I don't think Ulrich cares seeing his behaviour in the earlier seasons. (He was seen smoking and he got put in prison.) I definitely think the Magnus in Eva's world is meant to be straight edge -- we can see from the black x on his hand, he is into punk, and we see all of the posters on his wall. I think the creators of "Dark" meant the other Magnus in Eva's world to be straight edge.