In AWS, you can use Aurora to scale reads access over multiple instances. It's easy to setup and you can use scaling policies to follow your load. You need to check your billing, it's not the cheapest service.

Scaling horizontally is never trivial, can you share more about the requirements?

Usually application level partitioning, but it's hardly repeatable. Cloud providers offer solutions like Spanner, that cost quite a bit. You have new SQL DBs like yugabyte or cockroach, which are not exactly MySQL, and are not really battle tested. And noSQL like MongoDB or Cassandra, which are, well, not even SQL, but are proven technologies and scale quite effortlessly.