This is complicated. Depends on circuit.
”Scenario #4. What happens if the unmarried child of an LPR is over 21 using his or her biological age but under 21 using adjusted age on the date the petitioner naturalizes. The child cannot opt out of conversion from the F-2A category to the F-1, according to the BIA. So, the majority of children in this situation convert to the F-1 category. The July 2023 Visa Bulletin shows the F-1 backlogged about six years farther than F-2A using Chart A. Pity the practitioner who has to inform the family of this new development after representing the petitioner in the naturalization process.”
“But can’t the child argue that it is their adjusted age — not their biological age — on the date of naturalization that controls, and therefore they convert to the immediate relative category? That was successful in two federal court challenges. Tovar v. Sessions, 882 F.3d 895 (9th Cir. 2018) and Cuthill v. Blinken, 990 F.3d 272 (2d Cir. 2021). So, while the child in the F-2A category who is over 21 using biological age (under 21 using adjusted age) cannot opt out of automatic conversion to F-1, that child doesn’t have to opt out because he or she converts automatically from F-2A to immediate relative when the petitioner naturalizes.”
https://www.cliniclegal.org/resources/current-status-child-status-protection-act-calculating-adjusted-age-age-confusion