I have downloaded “the offline Help” and get the message The LibreOffice built-in help for current UI language (English (USA)) is not installed on your computer.
How do I get the English UK Help version
Your current UI language is US English.
You downloaded the UK help pack.
Switch the UI language to “English (UK)” under menu:Tools>Options>Languages.
If that UI language is not available, install the UK language pack and restart the office.