@Theera
Here is how to do in the way
@Erel proposed (taking what you was doing in another your work)
Dim myFont As B4XFont
myFont = xui.CreateFont(Typeface.LoadFromAssets("JSGiat-Bold.otf"),62)
SwiftButton1.xLBL.Font = myFont
SwiftButton1.xLBL.TextSize = 30
This is how to change Font and TextSize from code to the original SwiftButton.
I understand that it's not intuitive, but if
@Erel does not want to update the SwiftButton this is the way to go.