Yes it works.
It’s just if you use YARN_VERSION=1.21.1 and then you have a different yarn version (even transitive) in your dependencies, yarn seems to automatically pick the version of yur dependency (which may be different from the one you asked netlify to use). Afaik it’s on purpose and a yarn behavior, there’s nothing Netlify can do about it, just wanted to report this fact so that other people running into the same issue know how to solve it.