Atheist I know, claim they don't believe in the "supernatural", but I don't think there is anything more supernatural than nothing creating everything without a cause.

What could be more supernatural than that?

Life spontaneously emerging from  inorganic material unplanned and unguided.

That seems supernatural to me.

If anything a transcendent cause seems a very natural understanding. God isn't supernatural, rather without him there is no nature at all.

Romans 1:20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: