Glad to hear you got it sorted!
In the new plugin system, we use script type="module", which requires the correct CORS headers to be set. Old-style script type="text/javascript" do not require those headers.
We’ve been slowly migrating different systems to type="module" over the last few years. Themes were already using it, and so was highlightjs (which was the one in the other topic). Loading fonts from the CDN also has the CORS requirement.
So there were probably some other things subtly broken, even before the recent changes to the plugin system. Now that you’ve set the CORS config, everything should be working again 