Hi Goktug,
There doesn't seem to be a simple way to achieve this. You could upvote this idea I found but there has not been alot of activity on it: https://community.mendix.com/link/space/mobile/ideas/3506
What you are looking for is probably the style object TextStyle. From the docs: this property set will allow you to style text – using these props you can control text’s font, selection status, and more (the text property set also contains layout properties)
https://docs.mendix.com/refguide/mobile/designing-mobile-user-interfaces/widget-styling-guide/
https://reactnative.dev/docs/text-style-props