My understanding is that:
- no miles expire before 30 June 2025 for former SN amex cardholders
- miles earned before 30 June 2022 will expire at the end of June 2025
- from then, expiration starts rolling forward 36 months after issuance.

M&M Status also protects miles from expiring. And I wouldn't be surprised if the replacement card SN mentions also comes with a protection against expiration.

edit: Amex suggest it's actually end of June + one Quarter:
...alle award Miles ouder dan 36 maanden (ongeacht hoe ze zijn verdiend) komen te vervallen vanaf het einde van het kwartaal volgend op 1 Juli 2025...
...tous les Miles datant de plus de 36 mois expireront (quelle que soit la manière dont ils ont été gagnés) à la fin du trimestre suivant le 1er juillet 2025...