Good question. It has been debated for centuries whether or not Saint Paul wrote the Epistle to the Hebrews, but I’ve never heard any suggestion that anyone but Saint Luke wrote the Acts of the Apostles.
The opening of the Gospel of Saint Luke and the Acts of the Apostles are nearly identical and they are both addressed to Theophilus. It would seem that questioning the authorship of Acts would also entail questioning the authorship of Luke.
Yeah, I’m reading the salutation to Acts now. “The former treatise have I made..” Refers to Luke 1:3. Definitely written by Luke. I don’t know why anyone would disagree with it. Maybe something about it not “sounding” like Luke’s writing. I will take of the Bible says, though. Luke wrote it.