Steam deck compatibility?

I know you can add outside games to steam but would that make my pc Diablo IV work here or would I have to buy it again for steam deck?

I’ll play it again if it works but not if I have to repurchase.

You can install D4 on the Steam Deck without getting the Steam version. I’ve been playing it on an SD card on my Steam Deck since the game released! You have to either directly install Bnet from desktop mode, then install D4, or get a launcher client that makes it a bit easier to get bnet. I did it the direct method, then got art to add to my Steam profile for the game so it looks legit.

It’s kinda complicated, so I recommend looking up guides or videos.