The announcement Donovan linked to here appears to indicate that only council advancement personnel can log it for scouts at this point:
Council & District Advancement Chairs as well as Council Registrars (Eagle Scout app processors) will have the ability to allow the Citizenship in Society Merit Badge to count towards Eagle Scout for those few Life Scouts who started the requirements prior to the discontinuance date, and will complete the merit badge before Dec. 31, 2026.
ETA:. There’s also this update from the change logs:
https://discussions.scouting.org/t/april-6-2026-scoutbook-plus-updates/510106
