You go here: https://developer.apple.com/fonts/ (yes I know this is the official link - thing is: SF is a open type font, its just "hidden" deep in the downloaded package)
Then you download the font.
Then open the downloaded zip with 7zip. do all the following steps with 7zip:
- open the folder
SFPro
SFPro - open the
San Francisco Pro.pkg
San Francisco Pro.pkg - open the file
Payload~
Payload~ - open the folder
.
. - open the folder
Library
Library - open the folder
Fonts
Fonts
Here are all the fonts you need. BUT, for some reason, at least in my case, if I install the italics I can not choose the regular font in an application. I don't know why and haven't tried anything like renaming or such because I just found all of this. Which is thy I have not installed the italics at the moment. But the rest works just fine.
Hope this helps.
EDIT: With the converter, which @Tanno shared, I converted the font into .ttf
.ttf and it all works now.