Announcing your resignation publicly in advance may not be well-received by other companies. This notice should only be mentioned to recruiters when interviewing for new positions.

Instead, on your last working days, posting a thank-you note to the company for their support during your tenure will convey your appreciation for your former workplace. This also subtly indicates that you are open to new opportunities, thereby creating a better impression with both your previous and prospective employers.

This is just my opinion. I hope it can be helpful to you.