Wait a minute…so humanity started from inbreeding of Adam and Eve’s kids, and then in the flood of Noah the only people left were his family,

The first 11 chapters of Genesis and the book of Job are the oldest parts of the Bible..so more likely to have mythic elements.

This explains a lot of things (the second creation story looks like a Mesopotamian myth; the opening of Job has "God" looking like a petulant child like Zeus) and you can look to the overall message (God is somehow responsible for all of Creation) and that these stories tend to be "Just So" stories but with the twist if Æsop's fables: with lessons more important than specifics.

It's also why the timeline of the years per the Hebrew calendar is many orders of magnitude (~ 7) off from the scientifically-accepted age of the Universe.

Pretty much, though it does leave a lot unsaid, like just where Adam & Eve's sons found wives and if general boat-owners/fishermen survived The Flood but weren't Jewish and so didn't get into the book.

I think other humans were created at the same time as Adam and Eve but inbreeding is only really a problem if there are genetic defects.

Reads just like mythology.