Can I use Stevia instead of sugar?

To add to what halfpint said, here’s an article about baking with Stevia. https://stevitanaturals.com/how-to-bake-with-stevia/ According to the article, Stevia is 30 times sweeter than sugar, but the recipe includes weight measurement so it’s easy enough to divide by 30. You do have to add moisture and bulk— the article recommends applesauce— and watch the baking temperature. The article says that Stevia becomes unstable over 400 degrees, but I’ve seen that number as low as 355, so I'd probably bake them longer at a lower temperature—300-325– to be safe.

Maybe. Stevia is 200-400 times sweeter than sugar. So you would be using less stevia. That might be a bit of a problem since sugar is there for texture & moisture as well as sweetness. If you use less sweetener, the brownie might be drier.