At the moment we're using yarn v1 for package management in Theia's mono repository.

Yarn v1 is quite old and has a lot of known bugs. Even the yarn maintainers themselves advocate switching to the latest versions of yarn (v3 and/or v4) which uses different package management concepts by default. Since the introduction of yarn, the default Node package manager npm caught up in features and stability and is generally preferred. However there are also alternatives like pnpm which again uses a different package management concept.

It should be evaluated which package manager is the new best fit for Theia. Criteria are at least popularity, maturity, feature set, outlook in the future and migration effort for the Theia repositories and potentially downstream consumers. The choice should be validated with a POC before a final decision is made.