This title kind of implies that PG or MySQL aren't modern or modern enough which i think is is very wrong. Look what they bring in every update. I think they are quite modern!
I understood the question as:
> What can those newer database systems that are not beholden to RDBMS conventions do for us that Postgres and MySQL (and Oracle and SQL Server and DB2) can not?
Perhaps I'm misunderstanding your comment, but MySQL has definitely deprecated and removed features over the years. https://dev.mysql.com/doc/refman/8.0/en/mysql-nutshell.html