Are postgres connection able to manage multiple requests at the same time? I have an application using node Postgres driver to connect to my Postgres 12.
The pool size is currently 1.
Is it possible, for one connection, to have multiple requests sent before receiving the responses?
Figure two requests:

request A will last 10 seconds to be processed by the database,
request B will last 1 second.

If this is possible, that request B will be answered before request A?
No, you can only have a single statement executing at the same time on a PostgreSQL connections.
PostgreSQL v14 introduces pipelining of SQL statements, but that still means that one statement will execute after the other. Besides, I doubt that Npgsql already has support for that.
Use several database connections.