Due to a problem in the Intel® Quartus® Prime Pro Edition Software version 21.1, you might see this message when you launch the help pages from the Intel® Quartus® Prime Pro Editon Software graphical user interface (GUI). This problem only occurs when running on Windows operating system.
To work around this problem, open the Help page from the Windows Start Menu or open the Help page directly from your browser.
file:///<install directory>intelFPGA_pro/21.1/quartus/common/help/webhelp/index.htm#quartus/gl_quartus_welcome.htm
This problem is fixed starting with the Intel® Quartus® Prime Pro Edition Software version 21.3.