I very carefully and repeatedly tried following the step by step instruction as per the link. I now have the "save all" command in the quick access toolbar. It still will not work for me to change the default setting.
One peculiarity that I noted....
After having gone through the Font group setting choices, then clicking "default", I do get the message "do you want to change the default font to (font name). I clicked YES, however the next step says to click OK.
I am unable to click OK, because the moment I click YES to the message, the font page (with the OK button in the bottom right corner) closes before I can click on it.

Could this have any bearing on the problem? Any other suggestions, please?