The verb ἀποκαλύπτω occurs 26 times in the NT and its cognate noun ἀποκάλυψις 18 times.
BDAG provides a single meaning for the verb (very similar to the noun):
to cause something to be fully known, reveal, disclose, bring to light, make fully known
Within this meaning, the verb is used in various functions:
(a) in a general sense: Matt 10:26, Luke 12;2, John 12:28, Rom 1:17, 18, Luke 2:35
(b) especially of divine revelation of certain transcendent secrets (Ps 97:2, Dan 2:19, 22), eg, Matt 11:25, 16:17, Luke 10:21, Phil 3:15, 1 Peter 1:12. The revealers of Christ Matt 11:27, Luke 10:22; and the Holy Spirit 1 Cor 2:10, 14:30, Eph 3:5. For Gal 1:16 see V12.
two more instances are given in BDAG that we need no consider here.
Gall 1:16 should not be separated from V12:
12 I did not receive it from any man, nor was I taught it; rather, I received it by revelation from Jesus Christ ... 15 But when
God, who set me apart from my mother’s womb and called me by His
grace, was pleased 16 to reveal His Son in me so that I might
preach Him among the Gentiles, I did not rush to consult with flesh
Thus, Paul says he received his revelation of Jesus directly from Jesus. Whether he is referring to his road to Damascus revelation, or later personal revelations from Jesus, or both, is not stated. The important thing here is that Paul had a personal encounter with Jesus that changed his life, and the work of his life, forever.
Now, the "en" in Gal 1:16 is significant. Paul says that the personal revelation of Jesus he received was given in order that Jesus might be revealed "in" Paul and Paul's preaching. The "en" in V16 is "a marker of cause or reason, because of, on account of" (BDAG en 9).
Thus, Paul is saying that it was only a personal revelation of Jesus that enabled him to preach with such convicting power, to presumably live the kind of live required befitting a preacher of the Gospel and to show by example to those hearing his preaching what the Gospel meant. A great responsibility indeed.