Currently dotty and scala-3 are two different tags ("dotty" existed before, "scala-3" is a newly created one). And for each of them "Suggest a synonym" produces "Failed to propose synonym: Version specific synonyms can only be created by moderators".
A couple of quotes:
http://dotty.epfl.ch/docs/index.html
Dotty is the project name for technologies that are considered for inclusion in Scala 3
http://dotty.epfl.ch/blog/2020/09/21/naming-schema-change.html
Dotty becomes Scala 3
This article is a heads-up for the upcoming change in the naming of Dotty artefacts (as published to Maven). Currently, the organization name is “ch.epfl.lamp” which will become “org.scala-lang”. The artefact names will be changed from “dotty-xxx” to “scala3-xxx”.
This change will be part of the next Dotty release planned for October 1st which will be known as Scala 3.0.0-M1. We encourage maintainers of tooling (IDEs, build tools, ...) to prepare for this change now by special-casing the way they handle the compiler when its version number starts with 3. just like they already had to special-case versions starting with 0. to support existing Dotty releases.
Should "dotty" and "scala-3" be actually the same tag (synonyms)?
PRO. Mostly, users creating questions tagged with "dotty" or "scala-3" mean the same, namely discussion of new features in Scala.
CONTRA. Dotty is a compiler, Scala-3 is a language (more precisely, a version of language).
PRO. Dotty is the only compiler for Scala-3.
PRO/CONTRA. Dotty is not only the compiler but also the project name.
Possibly related discussion is at https://contributors.scala-lang.org/t/migrating-stackoverflow-answers-to-scala-3/3972
dotty
will be used after Scala 3 releases. Will it go away since the project is complete, or will it continue to be used to refer to the research version of Scala?