You're the first... boy version? Sorry if that's more weird! But also Hi! I'm Brigitte. I'm the official blacksmith for Skyhold per Hawke's approval, but I'm also a mechanical and bio-engineer. Which is kinda like your Dagna the Aranist, but with a technology twist! (I can't perform magic, just science that's advanced enough to kinda seem like magic)
So it's a bio-engineered arm, largely metal and fiber that can connect to and communicate with your nervous system. I'll need to resize it a bit for your body type and ensure it's symmetrical enough with your other arm, of course, but when it's done, it'll function just like a regular arm, but just stronger and more durable.