Your service worker (my website and where the service worker is) has a non-JavaScript content type: text/html. To fix, change the content type to a JavaScript content type, like “application/javascript”.
Other Information
The error keeps coming up when I try to install Arc. Is it something with Cloudflare?
Could you be a little more specific? You mention a server worker, what is that? If something has a MIME of text/html, and is supposed to be text/javascript you should make sure that the extension is .js (not .html), and any internal coding is set correctly (For example, no HTML DOCTYPE or other tags in the file).
Others have installed Arc successfully, so it does work here.