The examples that I gave work to show that God's laws are situational regardless of whether or not you agree that followers of God should follow what God has commanded in accordance with Christ's example.
In
Matthew 4:15-23, Jesus began his ministry with the Gospel message to repent for the Kingdom of God is at hand, which was a light to the Gentiles, and the Torah was how his audience knew what sin is (
Romans 3:20), so repenting from our disobedience to it is a central part of the Gospel message, which he prophesied would be proclaimed to all nations (
Matthew 22:12-14). Jesus also set a sinless example of how to walk in obedience to the Torah, so he would have still taught full obedience to it by example even if he hadn't repeated any of the commands in the Torah, and we are told to follow his example (
1 Peter 2:21-22) and that those who are in Christ are obligated to walk in the same way he walked (
1 John 2:6). So Jesus spent his ministry teaching his followers to obey the Torah by word and by example and He did not go to the cross or establish the New Covenant for the purpose of undermining anything that he spent his ministry teaching, but rather the New Covenant involves God putting the Torah in our minds and writing it on our hearts (
Jeremiah 31:33). Furthermore, in
Titus 2:14, Jesus gave himself to redeem us from all lawlessness and to purify for himself a people of his own possession who are zealous for doing good works, so becoming zealous for doing good works in obedience to the Torah is the way to believe in what Jesus accomplished through his ministry and through the cross (
Acts 21:20). Gentiles can look at what Jesus taught and decided whether or not to become his follower, but Gentiles can't follow him by refusing to follow what he taught.
I don't reject
Acts 21:25, but rather I just consider Paul to be a servant of Christ, so I don't interpret that verse as essentially ruling that Gentiles shouldn't follow Christ. Either Acts 21:25 contains an exhaustive list of everything that would ever be required for a mature Gentile believer or it does not, so it is contradictory for someone to treat it as being a non-exhaustive list by saying that there are obviously other laws that Gentiles should follow, such as the greatest two commandments, while also treating it as being an exhaustive list to limit which laws Gentiles should follow. Furthermore, Jesus said that all of the other commandments hang on the greatest two (Matthew 22:36-40), so if you think that Gentiles should obey the greatest two commandments, then you should also think that Gentiles should obey the rest of the Torah.
Our salvation is from sin and again the Torah is how we know what sin is, so if a Gentile were not obligated to obey the Torah, then they would have no need to repent from their sins, no need of the Gospel message, no need of salvation from transgression the Torah, no need of grace, and no need of Jesus to have given himself to redeem us from all lawlessness. However, the reality is that Gentiles are not permitted to do what God has revealed to be sin (
Romans 6:15).