The parallel collections were part of the Scala standard library in Scala 2.10 through 2.12, but became a separate module in 2.13.
The new version is published for Scala 2.13 and 3.0.0-M1.
release notes: https://github.com/scala/scala-parallel-collections/releases/tag/v1.0.0
In going from version 0.2.0 to 1.0.0, we broke binary compatibility, but in a way that is unlikely to affect most users. (See notes.)
The collections are documented at https://docs.scala-lang.org/overviews/parallel-collections/overview.html and https://javadoc.io/doc/org.scala-lang.modules/scala-parallel-collections_2.13