How can the virtual keyboard be enabled at the login screen?
On Windows it is really easy, but I haven't found to way of enabling it on a Mac.
There is a keyboard shortcut that propose you to access to Accessibility Options, and it is working at login screen. (Only on High Sierra.)
And for MacbookPro w/ Touch Bar:
fn-Opt-Cmd-F5 or Triple click on TouchID button
From this new window, you can click and enable the virtual keyboard:
Here is the Mac accessibility shortcuts ref from Apple.
EDIT 2: for macOS Mojave
If the problem is that you're not sure about your keyboard layout, try this:
Opt-Enter : It lets you enter the login in a clear text field. Use it to visually check your layout \o/
EDIT: (added information from comments)
I am sorry to say that this is not possible in Mac OS X unlike in Microsoft Windows. Maybe you could just wait for Apple to include it in their future releases. I hope I helped you :-)
The answer by itMaxence regarding High Sierra doesn't seam to be valid any more (perhaps apple changed something in one of the updates).
According to macOS User Guide, the Turn on accessibility options in the login window on Mac option seams to be available only on macOS Mojave 10.14
I can confirm that the accessibility options/keyboard is not working on 10.13.4 High Sierra when the screen is locked (login screen).
Actually it is possible OSX 10 allowed for onscreen keyboard in lock screen mode. I believe you have to sudo the root to enable it.
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