When did Libre Office Writer accessibility become freaking fantastic?

Point 1: same reason there's not an NVDA for mobile or Mac. It's developed by a community of volunteers, and they have all they can handle. It's open source, though, so anyone who wants to do it can, except that it would require a total rewrite in Swift.
Edit: well, ok, it's windows/mac/linux software written largely in C++. I suppose it could be spun out for IOS. But the point remains that it would be a heavier lift than the community has found worthwhile.
Which brings us to point 2....
Point 2. Libre isn't an ecosystem. It's a piece of Windows software. Any stand-alone IOS text editor not locked down to ICloud and a proprietary file format could do the job brilliantly. It doesn't need to be branded Libre. What's crazy is how hard it is to find a simple IOS text editor that can open a .txt file, much less .docx (which is an open format) without requiring ICloud or adding things to a proprietary library. It's the simplest thing in the world if only someone wanted to do it.
When I've tried Word mobile, it didn't have a single one of the features I listed and wasn't even as capable as OneNote (which is pretty capable, actually). I'm sure it's improved; but, at the time, it was useless from my perspective for anything more than a really short simple document, and, again, a free text editor that's like Notepad for IOS would be better, particularly given that Windows Notepad now does basic formatting using Markdown. Apple Notes now also imports/exports to Markdown, which makes it a free option, but cumbersome. Finally, Libre Writer is starting to have Markdown support, so there's a cross-platform potential. IAWriter is an example of a one-time purchase very capable IOS and Mac Markdown editor that doesn't require a library. I think those things point in the right direction for folks wanting to avoid 365 bloat and subscriptions, which doesn't need to be everyone.

I jumped up and down with excitement too fast. Tried some more stuff just now.
- Table navigation doesn't work, which I was expecting, but you can convert table to text and vice-versa, editing as plain text. I used to do that in Word anyway.
- Turns out comments are not accessible.
- I can't navigate to the footer area where the page numbers are. I suspect adding a running header would also be inaccessible (I couldn't figure out how to add one: the header menu only includes page number). It's possible I could be missing something, but I can't think of anything.
- When inserting a footnote, there's no way I can find to navigate back to the document without using the navigator, which only takes me to a heading or bookmark, etc. When trying to navigate back to the footnote text, I can't. The navigator takes me to where the reference is. The footnote number is not accessible, either.
Even all these things not withstanding, on the topic of professional use, keep in mind sharepoint and simultaneous collaborative editing, which Writer won't do.
I might still use Writer for my draft, because why not? But looks like the 365 subscription stays or will end up being restarted later.

on 2, the latest version of Thunderbird. Nothing new to report from the prior thread on Windows email clients. Sorry you had problems getting it up and running, but I think they were glitches rather than show-stoppers. Apologies if it wasn't you I'm remembering on that thread. Since you mention professional contexts, remember that it's limited on that score.
On 3, No, but if you have a Microsoft Exchange account, there's a basic integration with Outlook, which of course defeats the point. Apple is the kingpin of locking users into its ecosystem. I suppose you could use it online. I've tried like the dickens to find a way of getting some kind of cross-platform Notes alternative or integration to no ultimate avail. OneNote is a behemoth and too glitchy on Windows. When I tried Google docs last night, rotoring down by line separated the last character of the line onto a separate line (up by line worked fine), which is a problem I vaguely remember in IOS Ulysses using a keyboard, too, making it likely an Apple bug) I tried a lot of other stuff, too, like Drafts.
On 4, Except for the noted issue with headers, Calc looked promising. And, NVDA devs are well aware of the issue. It could be scripted around in Libre, I'm almost positive, and NVDA already accesses Word's object model for its implementation, so I think it's just a matter of doing something similar in Calc. I can also imagine a python script that could bind arrow keys to a routine that determined headers and voiced them through SAPI. I have some self-voicing macros I wrote in Word (by I, I mean Copilot). But to your point, I really doubt it. It's not easy to make a spreadsheet accessible, and I doubt it can be done without considerable work from the screen reader.

I'm unreasonably tenacious when it means I can procrastinate the actual writing. Turns out the Navigator pane is even more useful than I thought. There's a comprehensive context menu you can pull down on footnotes and comments to edit/delete/jump to, which is the way I found to toggle between footnote/comment text and the document. On headings, it allows moving sections up/down, too. All super straight-forward. Better UX than Word.
When inserting a comment, the text area is initially innaccessible. alt-tabbing away and back seems to do the trick to get at the comment text you're typing. The comment anchor seems to appear in the document as a non-Unicode character that isn't read, so it's a blank character. you therefore won't know from arrowing down that there's a comment, but you can use the Navigator, and fortunately fomments and footnotes appear as truncated versions of their text. So, I think it'll be pretty doable.
To see footnote numbers, check the option to show formatting marks.
I think that actually covers everything I'm likely to need--again, unless/until I go back to teaching; and, even then, I'll have free access to 365. I guarantee there are other gotchas, like knowing where images are inserted, but I don't do that for personal use.
In fairness, comments, footnotes, and headers/footers are far from straight-forward in Word. I spent half an hour getting page numbers into my template, and I'm still not positive they're in the right place.
Tangent alert:
I much prefer markdown, to the point I spent a month designing my absolute dream markdown editor--just a concept document. My plan is to wait until A.I. can do 90% of the coding while I learn enough Python to cover the debugging etc. I'm guessing a year might do the trick. The exciting part is that it would use inter-process communication to pipe information directly through a back channel to an NVDA add-on. Increasingly, I'm coming to the conclusion that if we want something done right for us, we have to do it ourselves. Accessibility is sliding all over the place as the pioneers retire and Gen Z and A.I. take their place as coders and PMs, IMO.
Unfortunately, Copilot is currently awful at coding, counter-intuitively enough. In fact, for every research question I throw at it, it's right about everything except everything I fact check. That's another discussion, though.

On the cross-platform simple notes solution front, Pretext does the trick for me. All I needed was a way to scribble my grocery list on Windows and take it to the store, plus similar simple tasks. The integration with Files as a default app is perfect, and the html preview of markdown a plus. I wish I knew what the touted "comprehensive keyboard shortcuts" were: there's no documentation, and hitting command key combinations does nothing.