Detect if `pg_crypto` in Postgres was built with strong random feature enabled
--disable-strong-random is a PostgreSQL configuration option available in the ./configure script in the source code. You could check to see if your version of PostgreSQL and the associated contrib modules were built with it by using pg_config --configure and looking to see if that particular flag was passed in as part of the config process. Though as it says in the thread that was linked, no reasonable production platform would use that flag, so odds are that you've got a cryptographically random build.