Unfortunately, there is no easy way to do that , you can check out comments in this forum question:
https://forum.mendix.com/link/questions/95403 (The only way to change the font is by adding it to the native template: https://github.com/mendix/native-template)
If you are looking for web app you can include custom family by defining it in the custom scss file like this:
@font-face {
font-family: 'YourFontName<to be used later in style>';
src: url('http://domain.com/fonts/font.ttf'); /*URL to font, should be something like '/font.ttf*, woff,woff2,eot etc
}
Please make sure that you have put the custom fonts in base folder.
First step is probably to add the fonts in native-template/ios/Fonts/ and native-template/android/app/src/main/assets/fonts/
In this https://docs.mendix.com/refguide/native-styling-refguide see 'TextStyle' and the reference to https://reactnative.dev/docs/text#style. This tells you how to set the font-family.