See here:
https://www.afkl.biz/trade/s/news-de...372&country=NL
As of 11 February and for travel as of 20 February 2025, Air France and KLM customers traveling on a Light fare ticket in Economy Class can no longer select or change a standard seat for free during check-in. If no seat is selected at a fee during check-in, Air France or KLM will assign a seat at no extra cost. Changing an assigned seat is possible at a fee. Customers traveling together will be seated together as much as possible.
This change does not apply to Flying Blue Ultimate, Platinum, Gold, and Silver members, Corporate customers (excluding bluebiz members), customers traveling in a group booking, and customers with disabilities. These customers can still select a standard seat for free during check-in.