On the newest version, you can tap anywhere on a comment to collapse. I like it because it's much more discoverable even if people figure it out by accident their first time.
I couldn't tell you 🤷 I'm not sure if it documented in Boost for Reddit either and I couldn't tell you how I'd discovered it at this point. But you're right, I'd say it's at least worth mentioning in the app description in the Play Store (though the number of people actually read those closely probably isn't high).