Yep. Paul told them to.
The church in Corinth was composed of probably MOSTLY gentiles.
1Co 12:2 You know that you were Gentiles, carried away to these dumb idols, however you were led.
And yet...
1Co 5:7 Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us.
1Co 5:8 Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.
Paul uses terms and concepts about Passover and the days of unleavened bread that they would not understand unless they were already keeping the feast. And by the way that word translated "keep the feast" means just that...observe one of God's holy days.
“Paul uses terms and concepts about Passover and the days of unleavened bread that they would not understand unless they were already keeping the feast. And by the way that word translated ‘keep the feast’ means just that...observe one of God’s holy days.”
The very passage you cited shows the Passover feast was being taught as a spiritual analogy. They “kept” it spiritually by practicing “sincerity and truth”. Much of what the apostles taught was from the Old Testament, but the main point was the spiritual application. Even the Sabbath has its application spiritually as a symbol of resting from our works and entering into the finished work of Christ. See Hebrews 4:9-10. When the author of Hebrews explains the symbolism of the furniture of the tabernacle, it does not mean that the Gentiles need to make a pilgrimage to Jerusalem to a physical tabernacle or temple. Christ taught in John 4 that the time would soon arrive (after Pentecost) when true worshippers would not be limited to special locations.
1 Corinthians 10:11 NKJV
Now all these things happened to them as examples, and they were written for our admonition, upon whom the ends of the ages have come.
The apostles were not sent to the Gentiles to convert them to Judaism. They were sent to preach the Gospel which was given under the dispensation of a New Covenant (as Christ implemented at the Last Supper).
2 Corinthians 3:6 NKJV
[God] also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.
The council in Acts made it clear that the Gentiles throughout the Roman empire were throughly familiar with Judaism and could have already converted if they had been led to do so. That was NOT the message of the Gospel. Rather, they were commanded to adopt 3 simple Judaic principles that were foreign to the Greek religions of the day but had ALWAYS applied to Gentiles because they predated the Law of Moses:
Acts 15:19-21 NKJV
Therefore I judge that we should not trouble those from among the Gentiles who are turning to God, but that we write to them to abstain from things polluted by idols, from sexual immorality, from things strangled, and from blood. For Moses has had throughout many generations those who preach him in every city, being read in the synagogues every Sabbath.
There was unanimous agreement to follow the council of James and Peter. Jews continued to follow the law of Moses as they always had done because it was written for the Jews. Gentiles were NOT commanded to follow the law of Moses. They did keep the ordinance of the Lord’s Supper with the bread and cup as in 1 Corinthians 11. Christ implemented this when He and the disciples observed the Passover celebration. The breaking of bread continued to be practiced apart from the Passover by both Jewish and Gentile believers. Sometimes breaking of bread was part of “love feasts” or community meals, but these were customs and not ordinances of the apostles, as is demonstrated by Paul telling the Corinthians to eat at home rather than bring divisiveness into the Lord’s supper. This is the closest thing the early church did together (Jews and Gentiles) that honored the symbolism of Passover. Gentiles did not offer a spotless lamb and put its blood on their doorposts.
There are only a few Biblical cases, to my knowledge, in which Gentiles were obligated beyond the council in Acts. One would be the example of Paul circumcising Timothy, whose father was a Gentile, but his mother was a Jewish believer. Gentile Christians might have observed the Sabbath when in the land of Israel because Gentiles were supposed to do this under the Law of Moses, but it does not apply to Gentiles generally. Nowhere in the entire Bible is there a command for Gentiles to rest on the Sabbath except when in Israel. Also, circumcision was given to Abraham to be for all of his physical descendants, not just Jews.
Paul specifically said the opposite of your claim about keeping feasts:
Colossians 2:16-17 NKJV
So let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths, which are a shadow of things to come, but the substance is of Christ.
Again, Moses gave us symbols and mere shadows. Christ is the substance. We no longer need the complex religious system God gave to Israel because we have Christ Himself.
“they would not understand unless they were already keeping the feast.”
Non sequitur - I understand those terms and concepts but don’t keep the feast.
“The church in Corinth was composed of probably MOSTLY gentiles”
Corinth had a large population of Jews.
“Christianity “ was/is a sect of 2nd temple Judaism.