Determining which biblical laws apply today.

[Seeking]

Many Christians claim that many laws/commands in the bible no longer apply today or do not apply to Christians. Can anyone quote scripture to defend that position. What guidelines (if any) does the bible give to determine what rules should or should not be followed.
Examples include-
Dietary laws, dress and appearance, sacrificial law, etc

Some people divide by Old and New Testament. Some people divide by laws of ritual and morality.

I have always questioned why people divide the laws the way they do and whether or not scripture states that some laws no longer apply. Please quote scripture to explain where the lines are. This is something I struggle to understand. Do we adjust to fit the modern era and dispense with much of the Old Testament, do we keep all the law, or only the law for the Gentiles? What does the scripture say? TIA