Glad you liked it.
Since Wm Leler was also asking for the development process, I answered in his response having in mind all your questions.
In Android the original author uses two ViewPagers. The front ViewPager has some padding so you can see three pages on the viewport. Then it has a handle that synchronizes both viewpagers when scrolling.
I took the same approach in Flutter with two PageViews but not taking any code from Android. The front PageView uses a fraction of the viewport (instead of the android padding) and there is also a handle to synchronize both pageviews.
But, just to emphasize, I couldn’t have done it without understanding how header rendering and pageview synchronization were done in the animation Gallery example.