F1 brings up a blank browser screen for on Mac 10.13

When asking for LibreOffice help using the F1 key, a blank browser screen appears with, for example, a URL of file:///Users/username/Applications/LibreOffice.app/Contents/Resources/help/index.html?Target=scalc/.uno%3AHelpIndex&Language=en-US&System=MAC&Version=6.2. What is missing?

I believe that’s tdf#121532, fixed in 6.2.1.

Did you download and install the “help pack”?

You can e.g. Select English (GB) or (US).
Of course it has to match your LO version.