The EntityManager doesn’t flush change automatically by default. You should use the following option with your statement of query:
@Modifying(clearAutomatically = true)
@Query("update RssFeedEntry feedEntry set feedEntry.read =:isRead where feedEntry.id =:entryId")
void markEntryAsRead(@Param("entryId") Long rssFeedEntryId, @Param("isRead") boolean isRead);