Hi,
>> I'm working with Autocad 2019 on Windows 10,
I have tried the same with AutoCAD 2019, cursor placed inside "AcadLine" (not even marked the whole word) ... and it's working well on my side.

As I don't see your cursor in your screenshot, try to click inside the word AcadLine (like you would do for adding a character inside that word), then press <F1> ... same result?
If the first attempt does not work, close the help and again press <F1> (I see this sometimes happen for AutoCAD help, where I'm starting a command, press <F1>, get the base site for help, not the command specific one .. then I close the help and press <F1> again and then it's working)
Another try: login with a different Windows user account, start AutoCAD (without any customization) and again try the same workflow.
- alfred -
------------------------------------------------------------------------------------
Alfred NESWADBA
ISH-Solutions GmbH / Ingenieur Studio HOLLAUS
www.ish-solutions.at ...
blog.ish-solutions.at ...
LinkedIn ...
CDay 2025------------------------------------------------------------------------------------
(not an Autodesk consultant)