Yep, and notice, it specifies what the first book was about, namely about Jesus and His actions and teachings. Plus both books are addressed to the same person. So it makes no sense to assume that Acts was written before the Gospel. To even be plausible, it would mean that Luke wrote a different Gospel first, then Acts, then the Gospel of Luke.
Very implausible. Look to the simplest answer.
Additionally, if Acts were written before Luke, then why were none of the questions left unanswered in Acts recorded? Acts leaves off abruptly with Paul in prison but alive, Peter alive, and the Temple still standing. Both men were soon martyred and the Temple destroyed. Why wouldn’t these be at least mentioned in the Gospel if it were written later?
Let’s look at the end of Luke and compare it to the beginning of Acts:
Luke 24:46 And he said to them, “Thus it is written that the Messiah would suffer and rise from the dead on the third day 47 and that repentance, for the forgiveness of sins, would be preached in his name to all the nations, beginning from Jerusalem. 48 You are witnesses of these things. 49 And [behold] I am sending the promise of my Father upon you; but stay in the city until you are clothed with power from on high.”
50 Then he led them [out] as far as Bethany, raised his hands, and blessed them. 51 As he blessed them he parted from them and was taken up to heaven. 52 They did him homage and then returned to Jerusalem with great joy, 53 and they were continually in the temple praising God.
Acts 1:1 In the first book, Theophilus, I dealt with all that Jesus did and taught 2 until the day he was taken up, after giving instructions through the holy Spirit to the apostles whom he had chosen. 3 He presented himself alive to them by many proofs after he had suffered, appearing to them during forty days and speaking about the kingdom of God. 4 While meeting with them, he enjoined them not to depart from Jerusalem, but to wait for “the promise of the Father* about which you have heard me speak; 5 for John baptized with water, but in a few days you will be baptized with the holy Spirit.”
6 When they had gathered together they asked him, “Lord, are you at this time going to restore the kingdom to Israel?” 7 He answered them, “It is not for you to know the times or seasons that the Father has established by his own authority. 8 But you will receive power when the holy Spirit comes upon you, and you will be my witnesses in Jerusalem, throughout Judea and Samaria, and to the ends of the earth.” 9 When he had said this, as they were looking on, he was lifted up, and a cloud took him from their sight. 10 While they were looking intently at the sky as he was going, suddenly two men dressed in white garments stood beside them. 11 They said, “Men of Galilee, why are you standing there looking at the sky? This Jesus who has been taken up from you into heaven will return in the same way as you have seen him going into heaven.” 12 Then they returned to Jerusalem from the mount called Olivet, which is near Jerusalem, a sabbath day’s journey away.
Notice that his description of the first book lines up perfectly with the end of his gospel.