I've resigned, manager wants it secret, I don't

[NoOneCaresInRealLife]

Exactly that really, I've resigned from my job end day was 31st December '20 but due to the nature of the business I've agreed to stay until 31st January '21 to help with transition. My manager has been calling people into the board room and telling them individually that I'm leaving and telling them not to tell anyone!
I am happy that I am leaving but this 'cloak and dagger' telling people has really annoyed me. I am part of the senior management team and in my opinion an email should have been sent out detailing my end date. I am quite angry about this stupidness
AIBU -

Control not co trip!

@NoProblem123

I’d just send out my own ‘loved working with you, all the best for the future email’.

What are they going to do about it

If they went to the trouble of writing it into the employees contract, and it could only have been divulged by the employee breaking the confidence of the boardroom, then a potential date in court.

I think the trouble with announcing too early, is that your authority and any decisions can be questioned or not taken seriously. Your position In the final weeks could become impotent before you leave.
Given your position the company need to let your external contacts know about future arrangements.
From the sound of it, and because you are not moving on to another job, I would hazard a guess your boss was hoping you would change your mind and has possibly been trying to find a way (albeit unsuccessfully) to make you an offer to stay on - this might explain the behind closed doors dIscussions with others.
Unfortunately because you are not moving on elsewhere the ‘spending more time with family’ could sound like you left under a cloud. I personally would sit down and agree a clear and unequivocal message about your departure.

How was the announcement?

Hi, well there wasn't an announcement as such. I casually dropped it into the conversation with my team and members of other teams that I've had reason to talk with. They all knew, which I knew anyway. One of my colleagues mentioned that my departure is already causing waves and people wondering what will happen going forward as my position is integral to so many different departments.

On a different vibe - my immediate manager keeps crying when talking to me about my leaving and had to leave the room when interviewing my replacement! 16 days to go

Your manager sounds like she’s nuts and depends on you too much, possibly can’t do her job.... good luck with the new role.