It uses JSONb under the hood. Just gives you a very "mongo" feel to using PostgreSQL. Not sure how I feel about it.
CREATE TABLE IF NOT EXISTS %I (_id UUID PRIMARY KEY, data JSONB)
Can they make it use uuid7 for ids for better insert_becomes_append performance?
Yes
Yes, I'm using JSONB underneath and translating the MongoDB syntax to native queries. As they're not super pleasant to deal with, then I thought that it'd be nice to use some familiar to many MongoDB API.
Regarding IDs, you can use any UUID-compliant format.