This is in LibO on Windows XP. The subject says it all, I think. There is a 'Help' button on this page of the Help dialog, but it does not bring up anything meaningful in Help when it is clicked. The Help page entitled "LibreOffice Calc Options" lists most of the Calc pages of the Help dialog, but does not include Formula. I would suggest that a Help page is written for this dialog page, and that the 'Help' button on that dialog page should be removed until this is done.
Sorry, too many mince pies. In the two places where I used the term "Help dialog" in the problem description, I did, of course, mean "Options dialog". (I can't see any way to edit the original description.)
Thanks for bugreport reproduced in 3.3.4 and 3.5.3 on Fedora 64 bit using English UI, local help reproduced in 3.5.2 on Windows 32 bit using Russian UI, online help Problem: button "Help" on dialog contains link to wrong page of help (needed help page I have not found) changing version to 3.3.4 as most early reproducible
Works for me, as I am redirected to the online help after clicking the help button. Version: 4.2.5.2 Build ID: 61cb170a04bb1f12e77c884eab9192be736ec5f5 Redirects to: Options page, where you can select "LibreOffice Calc" and then "Formula": https://help.libreoffice.org/Common/Formula_2