The strategy is to get you onto a different platform to make instant messaging easier. They are just "advertising" on Lemmy.
Once you're on a chat platform, they will likely attempt the "Romance Baiting" (formerly "Pig Butchering") scam: make the target fall in love, then persuade them to send money for things like "travel expenses" or "family medical bills". Also involves buying crypto.
A good guess but so far as i can tell they dont actually message people directly outside of the initial contact. The chat rooms are barely active but ive been idling on the matrix for days and nothing.