font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
Everything else is less user friendly. This loads instantly, looks perfect on the user's screen, and is guaranteed to look exactly as it's supposed to.
Not really.
By using a font like Inter UI you create the same experience for everybody, regardless of the platform.
Segoe UI, Ubuntu, Cantarell (Windows, Ubuntu, Gnome/Fedora) are within a different typographic category than San Francisco or Roboto, they're not even similar enough to each other. By using the system font stack you're basically fragmenting the user experience and look and feel.
Inter is a substitute for well crafted neo grotesque fonts loved by designers, like San Francisco (which itself is a better fitting alternative to Helvetica), it's of a similar quality.
As an aside, we will soon be able to use system-ui in place of a manually constructed font stack: https://caniuse.com/#feat=font-family-system-ui
On macOS and iOS specifically, the system font (San Francisco) has had a great deal of time and effort poured into readability — so much that rather than being a singular font, it’s a massive family of fonts or metafont with countless variants for various DPIs and use cases. For example, the “San Francisco” used for headings (h1, h2, etc) uses wider glyphs and more relaxed kerning, as is appropriate for headings and the “San Francisco” used for small text uses a variant that has its geometry tweaked to be more legible. It’s a free readability boost that all happens automatically when you use system-ui or -apple-system in your font stack. By using a custom font, you forfeit all of that.
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif
As I see it, this is very centric to a specific system and therefore does not offer the best user experience for everyone.