As a mod, they've put a lot of work recently into flagging trolls and astroturf accounts, and still have a lot of work to do. I run r/sanfrancisco, and wow there's a ton of bots and trolls flooding our sub about the Newsom recall.
They also seem to really want to find a way to monetize content in a new way. They've flirted with crypto and awards, but I imagine they have strong ambitions around how they can reward creators and moderators in a healthy, non-ad-based-way. (Their ads are the worst of all the big social networks, given how anonymous their base is. So they're forced to innovate, which I think is good for everyone.)
Plus the usual suspects (infrastructure, traditional demand gen marketing, paid moderation, etc).