So I'm a reddit refugee and downloaded Jerboa on Android. It took me forever to figure out how to login. I'm posting this in the hopes that it helps others.
On the Home screen I had to click on the top left hamburger menu. Them there was a down arrow in the upper right that I had to press before it said Add Login.
I hope this helps anyone with a similar issue.
I've played with Mastadon a bit in the past but not much. I didn't know you could comment with that account. Interesting...