‏I have set up Umbraco as a child application named "cms" under my website in IIS. However, I'm encountering issues with the site returning script errors. ‏Specifically, when I access the backoffice, I see 404 errors for resource loading, including JavaScript, CSS, and other files. The problem seems to be that Umbraco is installed under “/cms,” but it is attempting to load these resources from the root “/” instead. ‏I've tried several troubleshooting steps but have not been able to resolve the issue. Any assistance or guidance on how to fix this would be greatly appreciated.

This came up in a discussion just recently actually. Assuming this is Umbraco v9+ onwards, then using it as a child application isn't supported unfortunately. You can set it up as a child application in IIS (Not a Virtual Directory) and get the frontend of your solution to render out on a subfolder URL. But using the back office always still requires it to be at a root of a domain, so it would still require a second URL pointing at it to be able to use the admin side. Bit more here:- https://discord.com/channels/869656431308189746/1268191277418156144