With Windows in particular, you absolutely can navigate Windows + Office keyboard only. I do it every day.
Now, third party software, is always going to be all over the place. Stuff that was largely built on Win32 components works fine, but "modern" stylized applications rarely have strong support.
You’re right that lots of Windows apps were designed with Keyboard only workflows in mind. It’s a shame that MacOS has so many points where if you don’t have a mouse you’re out of luck.
There is one major improvement you can do on Mac, at least for menus:
I really feel like this used to be the default. That's how I always did it in macOS going back to the early 2000's.
Only in the last two versions or so did I notice it was no longer the default. I'm glad to see here that I can now re-enable it.
Edit: I see that I do have it enabled. But for some reason there are a lot of programs where it doesn't seem to work anymore, no matter what the settings. Off the top of my head: Half the Adobe programs I use for work.
I get that this might annoy you, but there is a direct trace all the way back to the original Mac in 1984 that required a mouse. As time went on and the two other OSes we still have gained mouse support (Windows, Linux) from their keyboard roots, they brought forward their ethos of keyboard navigation. Mac OS resolutely stayed attached to its mouse only roots.
That seems incredibly subjective. For people with carpal tunnel like myself, having to do everything on the keyboard can be very painful. The mouse alleviates that and gives visual feedback.
If you're interested in keyboard navigation of websites, consider a browser or extension with link hinting support! It worked really well in my experience a few years ago, although I've since became much more of a mouse guy and stopped using it.
Qutebrowser was my favorite browser for keyboard navigation but firefox, chrome, etc. have extensions for this as well.
I remember using TweakUI to enable "always show underline for shortcut key" because that genuinely felt like it should be a default for better usability.
I wouldn't say they're dead, just more hidden (e.g. GTK4 only shows them when you hold Alt). AFAIK most toolkits still support them, but app developers also have to actually define them.
On macOS with "Full Keyboard Control" you can navigate the system and most any official app from the keyboard. It's not an efficient experience though.
> you absolutely can navigate Windows + Office keyboard only
Unfortunately in Excel many operations can be done only with the function keys (e.g. F2, Shift-F8). I'd argue that leaving the center of the keyboard to press the function keys is not easier or quicker than reaching for the mouse.
Now, third party software, is always going to be all over the place. Stuff that was largely built on Win32 components works fine, but "modern" stylized applications rarely have strong support.