Unlike the other gospels, Luke begins his account with a description of what he’s writing and why. We can’t verify all of it (including the existence of the named recipient “Theophilus”), but much of the rest of it is easily confirmed. (I’m getting most of this from the section on Luke in Raymond Brown’s An Introduction To The New Testament.)

First, he describes the existence of other attempts to write down the gospel of Jesus in an orderly fashion. If the gospels of Mark and Matthew had not come down to us, we would have no way of confirming this, but the existence of other gospels (both canonical and non-canonical) show this to be accurate in his time period. Second, he specifically describes himself as an investigator and compiler, contrasting himself with eye-witnesses. Many Christians (in earlier periods and today) imagine all gospel writers to be eye-witnesses, but Luke’s description here is much more in line with what scholars think happened when the gospel writers composed their accounts. Thirdly, Luke describes his own account as “more orderly”, and when one compares Luke with a known source, the Gospel of Mark, and a reconstructed source, Q (as preserved in the gospel of Matthew), Luke’s account really does seem like he prioritized orderliness rather than, say, showing a fulfillment of prophesy (as Matthew does). For instance, he puts Marcan events in a more logical order in several places and removes Marcan doublets so as to reduce redundancy.

Given all that, the prologue to Luke’s gospel really does seem on the level. As Brown states in a footnote,

Although some have wondered whether the name “Friend to God” is purely symbolic for every Christian, the odds favor a real and influential person (or whom we know nothing else) who believed in Jesus or was attracted to what was preached about him.

Still, he allows:

In part, Luke may have chosen Theophilus as the addressee because his name could apply also to other desired readers.
One scholar who falls in the believers’ camp is David Allen who wrote Lukan Authorship of Hebrews. He argues for Theophilus being the high priest in Jerusalem 37-41 C.E. A former Sadducee. He also theorizes that Hebrews was written to a group of former priests who fled Jerusalem and embraced Christianity settling in Antioch. He dates Luke/Acts early. Which is cap.