As of now, Meta has not confirmed whether the blocking list for Instagram and Facebook will be merged in the January 2025 updates. Currently, blocking on each platform is separate, meaning users can block individuals on Facebook without automatically blocking them on Instagram and vice versa.
It’s possible that Meta may integrate the blocking system across both platforms in the future, especially with the growing integration between Facebook and Instagram’s backend systems.
For an official confirmation, it's best to stay tuned to Meta's announcements closer to the release date.