Remove monospace font from button on material components

I found the problem. It is not monospace font, it is letterSpacing. So I just add android:letterSpacing="0" on button to solve.

To update letterspacing globally for all your Buttons, you should use theming: https://material.io/develop/android/theming/typography/

You can redefine ?attr/textAppearanceButton in your theme to point to a different text appearance that has whatever letterSpacing you want.

Define the attr in your theme like this:

<style name="Theme.MyApp" parent="Theme.MaterialComponents.Light">
    <item name="textAppearanceButton">@style/TextAppearance.MyApp.Button</item>
</style>

And create a new TextAppearance Style:

<style name="TextAppearance.MyApp.Button" parent="TextAppearance.MaterialComponents.Button">
  <item name="android:letterSpacing">0</item>
</style>