Hi Samuel,
Thank you for contacting Syncfusion support.
The reported issue with “SfRichTextEditor throws exception while loading in UWP platform” is a Xamarin Forms framework issue, even with the latest NuGet version 18.2.0.59 SfRichTextEditor works properly with the lower versions of Xamarin Forms. The below mentioned MSDN link has been raised for the exception query, please refer the link for more details.
MSDN issue link:
As a workaround to fix the reported issue, we suggest you to downgrade the Xamarin forms version (4.5.0.617) and UWP target version to (10.0; 1776).
Kindly let us know if you require any further assistance.
Regards,
Devaraj S