TLDR: Shared indexes work with Coder + JetBrains Projector. To quickly prototype your project with shared indexes, you can generate them and host them as a dev URL on your workspace, for other workspaces to try.
After testing, you'll need to upload the contents of /home/coder/indexes/generate-output to a file server and use that as the index location, or include them in the Coder image's filesystem. Dev URLs are used simply as a test. You'll need to regenerate the metadata with cdn-layout-tool
with the proper destination as well.
Sourced from this tutorial: https://www.jetbrains.com/help/go/shared-indexes.html#configure-index-update