Two aspects of Acts 11 work violence against the historical reliability of the gospels.

1 – Acts 11:1-3 has the Jewish apostles and brethren very angry at Peter for having eaten in the house of a Gentile convert Cornelius.

1 Now the apostles and the brethren who were throughout Judea heard that the Gentiles also had received the word of God.
2 And when Peter came up to Jerusalem, those who were circumcised took issue with him,
3 saying, “You went to uncircumcised men and ate with them.”  (Acts 11:1-3 NAU)

2 – In Acts 11:18, after Peter explains his trance to the Jewish church, they respond as if salvation becoming available to Gentiles was some shocking unexpected theological development they’d never have guessed without God having given recent special revelation on it:

17 “Therefore if God gave to them the same gift as He gave to us also after believing in the Lord Jesus Christ, who was I that I could stand in God’s way?”
18 When they heard this, they quieted down and glorified God, saying, “Well then, God has granted to the Gentiles also the repentance that leads to life.” (Acts 11:17-18 NAU)

Why was Gentile salvation and fellowship so unknown even as late as the the time period of Acts 11:18?

Wasn’t it true that immediately after the calling of the 12 disciples, Jesus had a large ministry to Gentiles?

23 Jesus was going throughout all Galilee, teaching in their synagogues and proclaiming the gospel of the kingdom, and healing every kind of disease and every kind of sickness among the people.
24 The news about Him spread throughout all Syria; and they brought to Him all who were ill, those suffering with various diseases and pains, demoniacs, epileptics, paralytics; and He healed them.
25 Large crowds followed Him from Galilee and the Decapolis and Jerusalem and Judea and from beyond the Jordan. (Matt. 4:23-25 NAU)

There are several possibilities:

1 – “the apostles just didn’t get it” – in which case their fiercely screaming obtuseness impeaches their credibility as resurrection eyewitnesses, since it is after they allegedly see the risen Christ, that they are still harboring their anti-Gentile sentiment.  Acts 11:1-3.

2 – “Jesus didn’t really preach to the Gentiles” – wrong, see Matthew 4, supra.  

3 – “You need to be born again before you can understood God’s truths” – Ding! and the skeptics win by a knockout!

4 – “The controversy is not the possibility of Gentile salvation, but HOW Gentiles get saved” – wrong, read Acts 11:18, they find it shocking that God has granted to the Gentiles the repentance that leads to salvation.    It is their salvation per se, regardless of how it is achieved, that is the controversy.  They are not saying “well then, God has revealed that Gentiles can get saved by a single-step process…”  Also read Acts 11:1-3.  If the controversy was only over how Gentiles got saved, then the Jewish apostles in 11:1-3 would not have gotten angry with Peter so automatically merely upon information that he had eaten with a believing Gentile.  And since Acts 10:1-2 says Cornelius gave many alms to the Jewish people and was a devout believer, it is more than likely that the Jewish apostles of Acts 11:1-3 knew this truth about him, therefore, they were chastising Peter for eating with a Gentile Christian.

Finally, in Acts 10, God neither expresses nor implies that the Gentile-salvation message he is revealing, is a thing Peter had known previously.  Acts presents this revelation as a new thing God is doing.  That is, the author of Acts wants the reader to believe that before the time period of Acts 10, the church did not believe salvation of Gentiles was possible.

If so, then the parts of the gospels that indicate Jesus taught a gentile ministry to the apostles for three years prior (i.e., Matthew 4, supra) are surely fiction.

And since the risen Christ allegedly said the gospel was to be preached to the Gentiles (Matthew 28:20), a thing that in such Jewish context would naturally imply eating with and fellowship with Gentile believers,  the failure of Peter and the church between then and Acts 10 to recognize Gentile salvation also impeaches their credibility as resurrection witnesses.   They are hardly the “mightily transformed” people apologists typically characterize them as, for their refusal to acknowledge Gentile salvation.  Indeed, it seems they never learn anyway, read Galatians 2:9, they prefer to stick with Jews and allocate the entire Gentile mission field to Paul, despite the fact that the risen Jesus told THEM (i.e., the 11 original apostles) to evangelize Gentiles (Matthew 28:19-20).

For these reasons, any pro-Gentile sentiment found in the gospels is likely a fictional embellishment added at some point during the textually dark period between 70 a.d. and 200 a.d.