Could see one more DBS in the Mongo shell after connection

I am able to see one more DB by default, when executing

show dbs
admin
config
local

is the “config” db part of new version?

Yes
You will learn more about it in upcoming chapters(sharding,clusters)
From docs:
The schema of the config database is internal and may change between releases of MongoDB. The config database is not a dependable API, and users should not write data to the config database in the course of normal operation or maintenance