Page thumbnails and double page grouping
While reading, the horizontal carousel at the bottom of the screen shows your page thumbnails. Beyond jumping around the comic, long pressing a thumbnail is how you fix page grouping and share a page.
Double page grouping
When reading in double page mode, Panels groups pages for you automatically. It keeps the cover as a single page, starts grouping from the second page, and leaves any landscape page on its own.
That's the right answer for most comics, but not all of them — a missing or extra page early on throws off everything after it.
Fixing the grouping
Long press any page thumbnail and select Group from this page on.
That page becomes the start of a new grouping (placed on the left side for left-to-right reading), and the rest of the pages rearrange to follow.
In the example below, pages 2-3 are grouped initially. After tapping Group from this page on, pages 3-4 are grouped instead and page 2 is left on its own.

Sharing a page
Long press a page in the thumbnail carousel and choose share to send that page elsewhere — messages, notes, or any app in the iOS share sheet.
Want to pull text or a character out of a page rather than share the whole thing? Live Text lets you select text and subjects directly, including turning a subject into a sticker.