As far as TNG goes, a lot of the first contact stuff from S1 was a lot of already sufficiently advanced civilizations that are capable of at least local space travel and the Enterprise would openly announce like “Hey this is the Enterprise, we’re with the Federation, lets do diplomacy.” But whenever they interacted with less technologically advanced species they would usually do so much more covertly, wearing replicated disguises.
As far as TNG goes, a lot of the first contact stuff from S1 was a lot of already sufficiently advanced civilizations that are capable of at least local space travel and the Enterprise would openly announce like “Hey this is the Enterprise, we’re with the Federation, lets do diplomacy.” But whenever they interacted with less technologically advanced species they would usually do so much more covertly, wearing replicated disguises.