So currently you can only learn Hiragana, but are their plans to add Katakana (I mean to be able learn Katakana through Doulingo?)
I feel like Katakana should have as much attention as Hiragana, as in its own separate lessons, before diving into the "Intro" lessons. Going straight from Hiragana to Katakana and Kanji at the same time is overwhelming for a beginner. Personally, I used Duolingo to help me learn Hiragana and am having to pause and am learning Katakana through other means before I move forward on the tree. I would love it if Duolingo could add some Katakana sections after Hiragana!
There is a Katakana deck in Tinycards! (https://tinycards.duolingo.com/decks/29B5nanR/writing-japanese-katakana)
Katakana does not have a specific lesson, but is introduced in a number of the other lessons. You will find it in the lessons on home, restaurant, transportation, clothes, hobby2 and food2. You will be able to learn it here.