> Unless you’re referring to the screen reader
I am. I would never claim MacOS couldn't be used by professionals in a more general sense.
> but my impression is Apple is generally regarded as the best in what comes to accessibility features, and they keep improving. They’re so proud of it they frequently brag about it in promotional videos
For screen reader users, they're the best in terms of what they ship with the OS. You get a fully accessible experience out of the box, which includes a tutorial for first-timers. You can even run with text to speech in the Recovery mode e.g. to format your disks.
Contrast that with Microsoft, with Windows 10 being the very first version to offer an accessible setup/installation process, no obvious way to use a screen reader in Safe Mode, and next to nobody using Narrator in their day-to-day computer use because it took so long to be developed to any usable degree. One of the most popular Windows screen readers (JAWS) also costs hundreds of dollars - thousands over a user's lifetime if they purchase upgrades along the way. Apple are definitely winning there. Everything is free and just works, and I'm quite happy for them to brag about it.
Where it starts to fall apart is when you want to actually get things done outside of a core set of Apple apps. For example, Office support is pretty lacking, with poor or no accessibility for advanced word processing and spreadsheet features. The terminal support is so bad that an enterprising blind user made his own terminal screen reader to combat it[1].
There are other problems, such as the screen reader's slow performance making the entire OS feel sluggish. Plus, if there are any bugs in it, you have to wait for an entire MacOS update before it gets fixed. That's annoying when it's a Window Manager bug, but can be completely disruptive when your only gateway to your computer won't read your email for a while without crashing.
There are also tons of more opinionated stuff that users can (and do) argue about, like the efficiency of the way you browse the web with VoiceOver on MacOS vs the way Windows screen readers do it. But once you've assessed that the core accessibility experience isn't going to work for you, debating the rest is pretty pointless. Plus (and this is entirely anecdotal) it can become exhausting trying to have a discussion about these problems, only to have hordes of users tell you that you're wrong even though they're unemployed (or employed in a different field) and don't have people relying on them to get anything advanced done in the first place. Sometimes I think there's a tendency to want to justify how much money they've spent on expensive Apple hardware which, realistically, they didn't really need, especially if the cost of a cheaper Windows laptop plus JAWS would've been less or the same anyway. And these days, there's a fantastic free, open source screen reader for Windows[2].
[1] https://github.com/tspivey/tdsr
[2] https://www.nvaccess.org