> if you're an indie developer do you go with D or with Unity (which uses C#)?

You would have to weight this choice against existing engines like Unity/Unreal/Godot vs custom. I released a game with custom engine in D once and what really mattered was that there was no market fit (and no sales). Choosing engine vs custom is a question that only exists if people materialize to play your game ; a lot of successful game shops are prototype-heavy or at least advise that strategy.