The method to safely handle secrets in the networking.wireless module has been changed (PR #180872) to benefit from a new feature of wpa_supplicant. The syntax to refer to secrets has changed slightly and the option environmentFile has been replaced by secretsFile.
Only if you have been using networking.wireless.environmentFile a small migration is necessary: the instructions will show up in the nixos-rebuild output.
If you have any problems create an issue and ping @rnhmjoj.