It seems to me that Jesus made large chunks of Jewish law irrelevant for people of all nations by his sixfold "It was said . . . But I say to you" (Matthew 5:21-43).
The first ten chapters of Leviticus, and chapters 16-17, 20-27 are declared redundant by Hebrews 4:14-10:18, 11:9.
Mark (7:14-19) had seen that Jesus had swept away all the food laws of Leviticus 11, and he explained "Thus he declared all foods clean (Mark 7:12, see Acts 10:9-16). The permission to eat any kind of mammal, bird, reptile, and fish was given in Genesis 9:3, and Paul explains that "The law, which came four hundred years later, does not annul a covenant previously ratified by God, so as to nullify the promise" (Galatians 3:17). See Hebrews 13:9.
Jesus did order cured lepers to show themselves to a priest, just as we recommend that someone who is healed should check it out with a doctor. Otherwise Leviticus chapter 12-15 regarding skin conditions and uncleanness are totally ignored in the NT.
It therefore seem very unlikely that Leviticus chapters 18-20 have any relevance to us. These are only three chapters out of twenty-seven chapters of Jewish laws (no doubt very relevant to the 40 years wandering in the Sinai desert) which have been shown to have no lasting application to other nations.
(see the article "Why the Jewish
Old Testament?" on this website)