According to a web search, I should be able to drag a photo into a new position in the Photos app that is native to iPhone.
When I do that, the thumbnail moves when I drag, but when I release, it simply moves back to its original position. At no point do the photos rearrange themselves to accommodate the new position of the dragged photo.
What am I doing wrong? I have the iPhone SE. According to
Settings->General->About, the iPhone is running iOS 14.4