CSPA (Child Status Protection Act) does not apply to a filer's status changing from LPR (Lawful Permanent Resident) to USC (U.S. Citizen) because CSPA is specifically designed to protect the immigration status of children who might "age out" while waiting for their visa, and does not apply to situations where someone is already an adult and changing their status to a U.S. citizen; it only applies when a child's parent is petitioning for them to immigrate as a derivative beneficiary and they might turn 21 before the process is complete

I have been ready cases where the petitioner becomes a citizen after the beneficiary turns 21 and when they gets the interview they get denied because the category changes to F1.