Sabbath or "Shabbat", is Saturday.
So, if you are an Old Testament Jew, who is under the law, then rest on Saturday a little over 2000 yrs ago.
If you are a New Testament Christian, who has been "redeemed from the Curse of the Law", and are now "no longer under the Law, but UNDER GRACE"...
Then dont worry about days, feasts, seasons, penance, or trying to keep yourself saved.
Instead, Live your life for the Lord, worship God in sustained awe, and do not meet Jesus having never lead anyone to Christ.
In Isaiah 56:1-8, keeping the Sabbath holy is not just for Jews, but also for Gentiles. The way to act in accordance with God's righteousness is straightforwardly based on God's righteousness, not on any particular covenant, and God's righteousness is eternal, so any instructions that God has ever given are eternally valid regardless of which covenant is under, if any. As part of the New Covenant, those who do not follow those instructions in obedience to God's law are not children of God (1 John 3:10). Likewise, sin was in the world before the law was given (Romans 5:13), so there were no actions that became or ceased being righteous or sinful when the Mosaic Covenant was made or became obsolete, but rather the law revealed what has always been and will always be the way to do that.
In Deuteronomy 28:1-14, it describes the blessing of living in obedience to the law, while verses 15-68 describe the curse of living in disobedience to the law, so the law itself was not a curse, but rather it was given to teach us how to live in a way that God will bless, and being redeemed from the curse of the law is being set free to enjoy the blessing of living in obedience to it. In Titus 2:14, it does not say that Jesus gave himself to redeem us from the law, but in order to redeem us from all lawlessness.
In Romans 6:14, Paul described the law that we are not under as being a law where sin had dominion over us, which does not describe God's holy, righteous, and good law, especially because Romans 7:7 says that it is not sinful, but rather it is the law of sin where sin had dominion over us. In Romans 6:15, being under grace does not mean that we are permitted to sin, and sin is disobedience to God's law (1 John 3:4), so we are still under God's law. Furthermore, everything else in Romans 6 speaks in favor of obedience to God and against sin, so 6:14 should not be interpreted as speaking against obeying what God has commanded.
In Psalms 119:29, David wanted God to be gracious to him by teaching him to obey His law and in Titus 2:11-14, our salvation is described as being trained by grace to do what is godly, righteous, and good, and to renounce doing what is ungodly, which is what God's law was given to instruct how to do, so being trained by grace to obey God's law is itself part of the content of God's free gift of salvation, and participating in that training has nothing to do with trying to earn our salvation, but rather that is what it looks like to receive it. Our salvation is from sin and sin is disobedience to God's law, so being trained by grace to live in obedience to God's law through faith is what being saved from living in disobedience to God's law looks like. God's law is His instructions for how to live our life for Him, for how to worship Him, and for how to lead people to Christ, who is the living embodiment of the law.