sSet-enriched categories are one possible model for $(\infty,1)$-categories, by the work of Bergner and others. They are probably the most important model from the point of view of getting *actual examples* of $(\infty,1)$-categories. 

In fact, to give actual examples of $\infty$-categories in the model of quasi-categories, one uses various kind of nerves to get quasi-categories from various types of enriched categories, among which sSet-enriched are a notable example. 

For the model given by quasi-categories, also called $\infty$-categories following Lurie's terminology, there are very good references which develop the common 1-categorical notions in the higher setting, for eg. Kerodon, HTT, or the book by Cisinski. I haven't found a similar treatment for sSet-enriched categories. 



 - The approach of Riehl and Verity is particularly appealing to me, but if I understand correctly their synthetic theory does not apply to the model given by sSet-enriched categories, is this correct or am I misunderstanding?
 - Is there a reference which develops the basic theory for the model given by sSet-enriched categories? 
 - For example, what is an adjunction between $(\infty,1)$-categories
   presented by sSet-enriched categories? The naive guess would be that
   it is just a sSet-enriched adjunction? What is an equivalence?
 - If the synthetic theory of Riehl and Verity does not apply to the
   model given by sSet-enriched categories, are we in the situation
   where we have a theory well developed for some models, and some
   important actual examples can only be given by applying some functor,
   e.g. the homotopy coherent nerve to get quasi-categories from
   sSet-enriched categories?