> Run json_*() function on Internal Binary Format, which will serialize the Internal Binary Format to JSON as output

I don’t think that’s always correct (it is within this thread, which stated (way up) “if you’re always reading/writing the full blob”, but I think this discussion is more general by now). Firstly, it need not convert the full jsonb blob (example: jsonb_extract(field,'$.a.b.c.d.e'))

Secondly, it need not convert to text at all, for example when calling a jsonb_* function that returns jsonb.

(Technically, whether any implementation is that smart is an implementation detail, but the article claims this is

“a rewrite of the SQLite JSON functions that, depending on usage patterns, could be several times faster than the original JSON functions”

so it can’t be completely dumb.