The “gospel” changes at Acts 1-2. One way of saying this is the proclaimer became the proclaimed one — but this misses that John preached about Jesus, too. And Jesus’ own message was self-directed. But, still, a good point to be made: the preaching shifts to redemption in Christ in a direct and clear manner.

Acts 8:4 Those who had been scattered preached the word wherever they went. 5 Philip went down to a city in Samaria and proclaimed the Christ there.

Acts 9:19 Saul spent several days with the disciples in Damascus. 20 At once he began to preach in the synagogues that Jesus is the Son of God.

And this text by Peter says it all:

Acts 10:34 Then Peter began to speak: “I now realize how true it is that God does not show favoritism 35 but accepts men from every nation who fear him and do what is right. 36 You know the message God sent to the people of Israel, telling the good news of peace through Jesus Christ, who is Lord of all. 37 You know what has happened throughout Judea, beginning in Galilee after the baptism that John preached- 38 how
God anointed Jesus of Nazareth with the Holy Spirit and power, and how
he went around doing good and healing all who were under the power of
the devil, because God was with him. 39 “We are witnesses of everything he did in the country of the Jews and in Jerusalem. They killed him by hanging him on a tree, 40 but God raised him from the dead on the third day and caused him to be seen. 41 He
was not seen by all the people, but by witnesses whom God had already
chosen-by us who ate and drank with him after he rose from the dead. 42 He
commanded us to preach to the people and to testify that he is the one
whom God appointed as judge of the living and the dead. 43 All the prophets testify about him that everyone who believes in him receives forgiveness of sins through his name.”

The gospel that was preached was a gospel about redemption through Christ.

Speaking of changes, here is the “gospel/kerygma” according to Irenaeus (from Against Heresies 1.10.1):

The Church, though dispersed through our the whole world, even to the
ends of the earth, has received from the apostles and their disciples this
faith:

[She believes] in one God, the Father Almighty, Maker of heaven, and
earth, and the sea, and all things that are in them;

and in one Christ Jesus,
the Son of God, who became incarnate for our salvation;

and in the Holy
Spirit, who proclaimed through the prophets

the dispensations(6) of God, and
the advents, and the birth from a virgin, and the passion, and the
resurrection from the dead, and the ascension into heaven in the flesh of the
beloved Christ Jesus, our Lord, and His [future] manifestation from heaven in
the glory of the Father “to gather all things in one,”(7) and to raise up anew
all flesh of the whole human race,

in order that to Christ Jesus, our Lord,
and God, and Saviour, and King, according to the will of the invisible Father,

“every knee should bow, of things in heaven,, and things in earth, and things
under the earth, and that every tongue should confess”(8) to Him, and that He
should execute just judgment towards all; that He may send “spiritual
wickednesses,”(9) and the angels who transgressed and became apostates,
together with the ungodly, and unrighteous, and wicked, and profane among men,
into everlasting fire; but may, in the exercise of His grace, confer
immortality on the righteous, and holy, and those who have kept His
commandments, and have persevered in His love, some from the beginning [of
their Christian course], and others from [the date of] their repentance, and
may surround them with everlasting glory.