When it comes to designing REST services, Scala shines with tools like tapir because it allows you to reuse a lot of code between service endpoints, gives you automatic and perfect documentation, and everything is type-safe and checked at compile time. Not sure why you're looking into Scala, but for web services I see real practical benefits there.
I would advise against Play, mostly because it's a framework, its approach feels outdated, its future uncertain, and the documentation cannot compare with Akka. But with tapir the decision about the underlying library becomes a bit irrelevant, as it supports all the major players.
Besides web services, Scala excels at streaming. Especially for integrating with other services, I'd look into Alpakka. Again, the documentation is excellent. There are other interesting options for streaming, like fs2 and ZIO, but my experience with them is limited.
If you can give us some insights about your use cases, maybe we can come up with more concrete recommendations.
Finally, be aware that Scala is a powerful programming language which has a learning curve. I can recommend the courses on Coursera for getting into it.