Windows: hold `Alt` and type `0176` on the numeric keypad
Mac: press `Option` + `Shift` + `8`
Linux: press `Ctrl` + `Shift` + `U`, type `00b0`, then press `Enter`
iPhone/iPad: press and hold `0`, then select `°`
Android: press and hold `0`, then select `°`
Copy and paste this symbol: `°`