Hi, I have set 1.9em of line-height for texts in the customizer and it is appearing fine in the frontend. But I do not know why it is not applying in WordPress Gutenberg editor (screenshot.)
It’s because GP has CSS which defines the editor style.
Can you try add .editor-styles-wrapper p as the target element in customizer > typography to override the GP editor style? Please refer to the screenshot below: https://www.screencast.com/t/IxMZtH1oEBjT