Use More Force
That's essentially what this boiled down to. I was correct that this is a self-extracting crank and I was performing the steps that should have worked. More force was required.
@JoeK and @Carel were both correct. @JoeK was right that there was indeed a very loud and obvious "snap" when it finally loosened, and @Carel was right in that having a foot on the opposite pedal was helpful.
In the end (don't try this at home) I found more force by reattaching the drive side pedal and using my large
8mm wrench as the non-drive side "pedal". I leaned against a wall, mounted the bike (at risk to myself), stood on the "pedals", and did what I could to apply force with my body weight. Eventually, things did come loose, but there was a risk of injury when it suddenly gave way. I almost lost my balance and fell. Having a helpful friend would have been better, but I was on day three of struggling with this and impatient.