Ok, then probably you need to do what this article mentions for Emmet - for HTML server. The issue is that the HTML server is not started for .heex.html files, so actions specific for HTML are not run. The key would be to force HTML server to start on HEEX files.
Well, they are. Syntax highlighting works. Elixir language server starts. It does not claim to provide same capabilities as with plain HTML files. Perhaps this is a discussion better suited for some Zed forum or issue tracker.
Mainly Emacs.
