It is possible to do that, but your site in the subpath needs to be aware of being in a subpath, and all the links in the HTML need to have /staging as a prefix.
Since you’re using Hugo, there’s likely a way to configure it to generate URLs with a prefix everywhere. I think there’s a baseURL option you can configure.
That said, a subdomain is certainly the easiest solution.
That’s a pretty old version at this point. Please upgrade to the latest version, 2.7.5.