So, the 14th Amendment protects “privileges or immunities.” There’s some of historical evidence of what those might include. But in the Slaughterhouse cases, the Supreme Court drained the phrase of any legal significance. There are many legal scholars across the political spectrum who think the Slaughterhouse cases are inconsistent with original public meaning.
Those scholars who think Obergefell, Roe, and such are consistent with original public meaning tend to say that “substantive” due process should be understood as code for “privileges or immunities.”
It’s a controversial position that natural rights are what the Constitution protects, even among legal scholars who think the Constitution should be interpreted according to original public meaning (most “originalists”).