Hi Rafael,
Greetings from Syncfusion.
We have tested customizing Increment and Decrement button by setting font icon, font size and font color and the sample working properly in 17.3.0.21 and latest 17.4.0.40 version with Xamarin.Forms version 4.4.0.991265.
Find the version and device details below.
· Android version 9
· iPhone 11 pro max iOS 13.1
· Windows version 1809 OS build 17763.914
We suggest you check the attached sample. If you still get issue, please provide us version, device details and modify the above sample which would be more helpful for us to assist you.
Thanks,
Rachel.