Derek Sivers wrote in 2015 about merging more of the business logic into postgres, including generating JSON in postgres [0]. I've personally used this approach and found it quite powerful. There may be downsides to that approach if somebody else is going to be maintaining the project and doesn't understand postgres too well.

There's also PostgREST[1], which exposes a REST API to a postgres database and has been discussed on HN before [2,3]

[0] https://sivers.org/pg [1] https://postgrest.com/en/v4.3/ [2] https://news.ycombinator.com/item?id=13959156 [3] https://news.ycombinator.com/item?id=9927771