1. 'Their Feasts' should be taken in context: They were not honoring God has he intended in His Feasts and festivals, and that should be taken in context. A verse taken out of context is often used as a pretext to spin the Scripture.

https://www.biblegateway.com/passage/?search=Isaiah%201&version=AKJV

The WHOLE CONTEXT is needed for accuracy here: The issue is not the feasts themselves, because the Feasts were Biblical. The issue is : Don't keep the Feasts and call them mine if you are disregarding the rest of the Law, especially what we would call the moral law as Christians.

2.Jesus kept all the Law, both Moral and Ceremonial, granted. There were, however, Jews who sought to keep both the Moral and Ceremonial law rightly, there were even kings who sought to: Josiah, Hezekiah, Joash, Jehoshaphat.

3. There is good evidence from Acts that the believers were still keeping the Feasts and Festivals:

The following Jewish feasts and festivals are alluded to or directly mentioned in the New Testament:

Passover (Pesach): Mentioned in Matthew 26:17-29, Mark 14:12-26, Luke 22:15-20, and John 2:13-23, 6:4, 11:55-19:14.

Unleavened Bread (Chag HaMatzot): Implied in Matthew 26:17-29, Mark 14:12-26, and Luke 22:15-20, as part of the Passover celebration.

Feast of Weeks (Shavuot/Pentecost): Not explicitly mentioned, but alluded to in Acts 2:1-47, where the disciples receive the Holy Spirit on the day of Pentecost.

Feast of Trumpets (Rosh Hashanah): Not explicitly mentioned in the New Testament.

Day of Atonement (Yom Kippur): Not explicitly mentioned in the New Testament, but alluded to in Hebrews 9:1-28 and 10:1-39, where Jesus’ sacrifice is compared to the Levitical system, including Yom Kippur.

Feast of Booths (Sukkot): Mentioned in John 7:2, 14, 37, as Jesus attended the festival in Jerusalem.