The functionality of this theme component has now been merged into Discourse core.
https://github.com/discourse/discourse/commit/d51baa3bb3b08c5a7df6c22593d0162be6543147
To enable it, change the “page_loading_indicator” site setting from “spinner” to “slider”. For now, the old ‘spinner’ remains the default, but we may revisit that default in the near future.
Admins on sites with the old theme component will be shown a prompt to uninstall it:
