I've grown accustomed to the font apperance in Joplin and I'm now trying to emulate it in another application. I have the "Editor font family" left as blank in appearance settings, and it's stated that:
If not found, a generic proportional (variable width) font is used.
I searched the forums, and found a post by uxamanda regarding this:
I checked the default font for macOS Catalina (which I use) and it supposedly SF Pro Display. I tried downloading the font and compared it directly with Joplin but they differ.
Does anyone have any insight into what font is used? Here is a screenshot of how the default font looks for me in Joplin version 2.8.8:
The same font may look different depending on the application. Specifically, Joplin uses Electron (Chromium) for rendering, and the same font rendered by it won't look identical to the same font rendered e.g. by a native OS application. Chromium itself is known for using custom, non-native font rendering.
Depending on what area of the application you are using and what OS it can use different fonts.
To check exactly you can just use the dev tools (Help > Toggle development tools).
Press the little button on the top left of the new window/panel that popped up and hover over the text you want to check.
I think by default the editor uses Avenir on macOS with Arial as the first fallback then the default sans-serif font (e.g. on Linux Mint it goes to Ubuntu).