Testing this using Ubuntu with the latest Chrome browser, I’m getting the following error on my local dev site:
component-templates.js:54 [discourse/theme-10/discourse/templates/components/conditional-loading-spinner] conditional-loading-spinner was authored using gjs and its template cannot be overridden. Ignoring override.
On my production site, also testing with the latest Chrome browser on Ubuntu, I’m not getting errors, but also am not seeing a loading spinner.
I think some changes have been made to how templates get overridden in themes since this theme component was released: Overriding Discourse templates from a Theme or Plugin. I think the way Discourse implements the loading spinner has also changed since then.