I don't use the triangles. If someone else uses them, good on them. I personally have the margins set to 4/4/4/4 which makes it hard to hover on the margin for any length of time and makes the triangles miniscule.
Not to mention I seem to remember a discussion back in October where the OP did not want the triangles-- ah, there it is.
Calibre 4 Ebook Reader -- Don't Show "Next," "Previous" Triangles started on Oct. 3rd, 2019.