I can confirm this error. It used to work but not anymore and that's a pity because the Packages Help function is a great tool! I'm working with Windows 10 Home with TeX Live 2017 / W32Tex and TeXstudio 2.12.6 (hg 6632:7777b2b8a906) Using Qt Version 5.9.1, compiled with Qt 5.9.1 R Now I'm not an expert, but as I use this version of Texstudio for some time and the function we're discussing stopped working some time after the last upgrade of Texstudio (if I'm not mistaken), could it be that the problem...
No, the correct link should point to https://www.texstudio.org/ (also secure http)
URL in Help Menu in http format, instead of https
Textfont parameter