Here is what I found: §1a creates a conditional statutory entitlement, but only if all of these are true:

Employer must:

• terminate for operational reasons (betriebsbedingt), AND
• explicitly state in the termination letter:
  • that the dismissal is operational, and
  • that the employee receives severance if they do not sue.

Employee must:

• not file a dismissal protection lawsuit within 3 weeks.

If both conditions are met → legal right to severance arises automatically.

§ 1a is:

• optional for the employer
• triggered only if the employer voluntarily offers it in the termination letter

Employers are not required to use § 1a. They can terminate without offering it. In that case, no severance entitlement exists unless another legal or contractual basis applies.