Acts 17 presents a clear "picture" of what language was used in the OT "manuscripts" searched in the early church.
Act 17:11 These were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so.
Act 17:12 Therefore many of them believed; also of honourable women which were Greeks, and of men, not a few.
You state there is a clear picture stated in Acts 17. I assume you mean Greek as that is something you highlighted in the verse. However, it is quite clear that the word translated as "Greek" is referring to type of people group and not the language of the scriptures they were diligently searching. There is not an absolute statement here as you seem to be suggesting.
As with most things, an accurate understanding comes from investigating the entire subject, not just a single verse. Luke is very particular in describing classes of people who he is referring to. He is consistent through the entire book of Acts.
Ioudaîos - Jews, ethnically Jewish -
https://www.blueletterbible.org/lexicon/g2453/lsb/mgnt/0-1/
For example Acts 17:17
sebo hellen
God-fearing -
https://www.blueletterbible.org/lexicon/g4576/lsb/mgnt/0-1/
Greeks -
https://www.blueletterbible.org/lexicon/g1672/lsb/mgnt/0-1/
Those other than Jews; that is, gentiles. Not necessarily ethnic Greek. But in general, people of the world. But represented as Greek since that was the lingua franca of the Roman empire.
For example Acts 17:4
Sometimes Luke refers to them as proselytes - those gentiles who adopted Judaism.
God-fearing proselytes as in Acts 2:10, Acts 13:43
G4339 - προσήλυτος prosḗlytos, pros-ay'-loo-tos; from the alternate of ; an arriver from a foreign region, i.e. (specially), an acceder (convert) to Judaism ("proselyte"):—proselyte.
www.blueletterbible.org
The narrative in Acts 17 is describing the difference of behaviour to the Gospel in two cities - Thessalonica and Berea.
[Act 17:1-2 LSB] 1 Now when they had traveled through Amphipolis and Apollonia, they came to Thessalonica, where
there was a synagogue of the Jews. 2 And according to Paul's custom, he went to them, and for three Sabbaths reasoned with them from the Scriptures,
...later...
[Act 17:10 LSB] 10 And the brothers immediately sent Paul and Silas away by night to Berea, and when they arrived, they
went into the synagogue of the Jews.
...and even later in Athens:
[Act 17:17 LSB] 17 So he was reasoning in
the synagogue with the Jews and the God-fearing [Gentiles], and in the marketplace every day with those who happened to be present.
...and even more later:
[Act 18:7 LSB] 7 Then he left there and went to the house of a man named Titius Justus, a God-fearer, whose house was
next to the synagogue.
Always connected with the synagogue in each of the particular areas. Always with Jewish culture.
The particular verse that was referenced: [Act 17:12 LSB] 12 Therefore many of them believed, along with not a few prominent Greek women and men.
It's actually saying that many of the Jews in the synagogue believed. "Along with", as in, a number of lesser amount made up of prominent women and not a few Greek (gentile) men. (I state the adjectives this way as that is what the Greek texts actually states).
This passage can not be used to give evidence that the Old Testament in Greek was the main language that was being searched by these believers. Evidences of what language was in use has to be built up in other ways, but that is not the point of this comment.
