Download the JetBrains Mono from the Github, and there is JetBrains Mono and JetBrains Mono NL in the ttf folder. What the difference between JetBrains Mono and JetBrains Mono NL?
JetBrains Mono NL is the no-ligatures version of JetBrains Mono font.
In some editors you may have difficulty disabling font ligatures (although some popular editors like Sublime Text, VS Code do have the option, e.g., VS Code's "editor.fontLigatures": false option). If you don't want font ligature, you can simply use the NL version.