Instagram doesn't claim to be a "free speech" platform. You have to only be mildly interested in it to see that it's all about "engagement" Parler explicitly claimed "free speech" as a goal
The "simple promises" from JS are (somewhat crippled) copies of Futures from other languages. In Scala the results of those futures can be produced at the same time, even if they are purely computational as Scala and most other languages are both asynchronous AND concurrent.
So their docs seem pretty clear that their lambda engine runs jvm based languages. Or at least java and scala, but if you can run java you can run scala and clojure and jruby etc.