A standard rigid seatpost is still a solid choice for certain gravel riders. If you're primarily riding smooth gravel roads, racing where every gram counts, or you naturally stand on descents rather than staying seated, a rigid post keeps your bike light and simple with nothing to maintain or malfunction.
That said, you can still squeeze out some comfort. Carbon rigid posts naturally absorb more vibration than aluminum ones, and the seatpost diameter matters more than most people realize—a 27.2mm post will flex noticeably more over bumps than a thicker 30.9mm or 31.6mm post, giving you a bit of free compliance.
Just know what you're giving up: no on-the-fly saddle height adjustment for technical descents, and no built-in shock absorption for long, rough days in the saddle. If your gravel adventures lean toward chunky singletrack or all-day bikepacking on rutted roads, you may find a rigid post leaves you wanting more comfort and control.