If you haven’t signed anything, then nothing is enforceable.
Please do not sign anything, ever, unless you understand the document completely and are sure it provides a strict benefit to you. If you do not understand it, then please consult a professional unrelated to the company.
In fact, there is no reason to sign a document promising your previous company anything if you have already secured your next job.
How can you benefit from signing such a document? Even if the agreement is unenforcible, why would you make it in the first place? At best they don’t follow up, at worst you have to waste your time getting any calm against you dismissed. How does that help you in any way?
Signing a contract with a non compete clause when starting a job is a different matter, but still one to consider. However, signing anything when leaving is a foolish move without proper compensation.