I had an employee with me for 25 years who gave two weeks notice two years ago. I was shocked and it was poor timing for me, but life goes on. I took it very well, which I later learned really hurt her feelings. She apparently thought I’d be devastated and beg her to stay. (I heard all this from a friend of hers.)
My uninformed advice: based on how you’ve described the company (mass layoffs, unpleasant atmosphere), it sounds like they may be circling the drain. Unfortunately, in that situation managers and coworkers can become very unprofessional. Recognizing what your departure will mean for their workload, they may try to guilt or pressure you into unreasonable asks.
All I can recommend is being polite and firm. Your final day is X date. You will complete the work you reasonably can in that timeframe. You will work with your supervisor to bring whomever he/she desires up to speed on your duties. But your assistance with the transition ends when you leave the company.
OP, can I recommend this site “Ask a Manager”? This is one fairly common and significant topic that people have asked about and that she’s discussed. The link will bring you to a list of exit interview discussions (below a list of ads related to exit interviews):
Good luck! Please update because I’m invested 
Happened to me once. The boss called me and another guy in on Friday afternoon and handed us our termination letters with no explanation. An HR guy walked back to my office to get my stuff, and I thought I’d clear out miscellaneous emails, only to find they had locked my account while I was in the meeting. The guy was a real prick, but I got paybacks several months later.
LOL! i told my boss, he was actually very cool about it (i think in the back of his mind he’s thinking “Great! Cost savings!”)
word got out insanely fast and i’m trying to control the leak but so far you were all right, it’s been much less painful than i anticipated. 50% have been “cool i’m happy for you!” and 50% have been “i’m happy for you but what am i gonna do without you?” so i guess i get the flattery and the support without too much of the negative emotions. maybe that’s still to come 
HR for their part – who has actively avoided giving me the time of day for all of 2023 – has been very on top of things with this news haha
Congratulations on getting it over and done with. I recently retired, and went through the same anxiety. I had worked there for twenty-three years, and it was hard to wrap my head around the idea that I wasn’t going to be there anymore. When I told them, I too got a lot of “I’m happy for you”, “I’m jealous of you”, and “What’ll I do without you?” from my various bosses.
Yay! Glad it’s over and it wasn’t too bad. Enjoy yourself as you embark on a new adventure!
thank you all for your support today! it’s been an exhausting day already but as usual the worrying was way worse than the reality
Congratulations on your unemployment!
Like I’m fond of pointing out to short-time co-workers, “What are they going to do, fire you?”
Don’t sweat it- you will have already quit, and you don’t owe them anything. Not even to put up with their bullshit if they take too long, delay you, etc… You’re doing this as a nice thing for them, not for yourself, so you need to keep that in mind if they act like you owe them anything at all.
Congratulations.
Amaguri, there is some good advice here, especially about clearing out the stuff you want and completing stuff that is important to you before you give notice. That includes contact information for those you want to stay in touch with. Because you never know. As a general rule, I prefer to not burn bridges but being light and not completely honest with HR can actually be a boon to you, should you ever find yourself wanting to come back to this company. Because they may yet turn things around. But good for you for not sitting around and waiting for that to happen.
Best of luck to you.