Preface:
I am a fan of accessibility overlays, especially when they can be used to reduce the usage of the mouse pointer to control you computer.
Now with the release of macOS Catalina, I think the new "grid overlay" and "numbers overlay" should be mapped to the keyboard as well.
Imagine typing in Mail, then switching application and tabbing to the browser, and only with the keyboard, navigating the application!
How can I invoke macOS Catalina "Voice Control" features using only the keyboard?
How can I control my mac with keyboard only?
Best Answer
On controlling mac with only keyboard, I have a couple of really lame/impractical solutions that you probably already know about.
There is System Preferences->Keyboard->Shortcuts. There, you can use an unfriendly ui to configure a quite few undocumented options, mapping them to keyboards strokes that only sometimes work. If you spend enough time memorizing shortcuts, you may get somewhere with mouseless use of your Mac.
Then there is System Prefs->accessibility->switch control. Click enable switch control check box. A black window will pop up. Click on Pointer. That gives you a bunch of options to simulate mouse use by pressing just space bar. If you map turning this option to a keyboard shortcut -- BAM! You can do anything without a mouse. The downside is it takes like 30 seconds for every click.