Massachusetts -- Boss Threatened To Change My Resignation Date Unless I Supply Him A Document Of Exactly What I'd Be Working On Up Until My Resignation Within 30 Minutes

Work at a large company and I put in my notice. In fact, I didn't even explicitly put in my notice, I told my boss I had an offer and said I wanted to understand how PTO would be paid out with the pay structure of my job, as that would affect my last day.

There was a long discussion with HR where it basically came out it would be more advantageous for me to use my PTO then put in my resignation (basically, my pay includes a signing bonus payment that won't be paid out if I leave, but will be paid out if I use the PTO). My boss said he won't allow that, and that I've "already given my resignation", despite the fact that I never officially sent the email, I simply told him I had an offer elsewhere (which I didn't even say I signed). He then told me to either send my resignation or he would put it in for a specific date and time that he chose two weeks out

Later, after this whole event, there was an optional meeting which I don't usually attend and didn't accept on my calendar. My boss messaged me angrily saying I need to be in this meeting because I am the "expert" in some technology. I am by no means the expert in this technology, I have probably used it for a grand total of 4 hours. I never attend this meeting, so I didn't understand what he was so heated about.

He then started saying he needs me to write up what I will be doing for the remaining time before my resignation date within the next 30 minutes and send it to him, otherwise he'll "change my resignation date" to earlier because there's "no point in me being on the team". This seemed incredibly suss to me. I asked him multiple times, "is that not just firing? Are you firing me?" and he kept dodging the question and never answering it, instead just reiterating that I'd better get that document to him in 30 minutes

I started questioning the actual exercise, like "what if I don't finish what I say I'll finish before my resignation time?" and "what if you don't approve of what I write?" and he just kept saying "this isn't ambiguous, just do what I say right now" and re-iterating the ticking time bomb of it, saying like "you have 10 minutes to get it done"

I felt this was also a bit manipulative because this was during a non-optional meeting, so I felt I'd be screwed either way. Either I write this document, or I miss a meeting that I'm supposed to attend.

What should I do here?