Currently the only RTF in SmartSuite is SmartDoc which will connect in Softr to display rich text. However you can't update SmartDoc fields via Softr which is problematic for creating a portal or admin interface. Softr has a Rich Text Field, but it will only map to SmartSuite's Text or Long Text fields, and doesn't preserve the formatting created in Softer when updating the record in SS.
I love the functionality of the SmartDoc field within SS, but adding an RTF field would be really useful for mapping integrations via Fillout, Softr and Relay.