It is a little hard to say exactly what might be going wrong given this description, but it is a good sign if you can see that HTML files are emitted in the output path after running that command. There is no "root" page for DocC output at the moment, so it might be possible that you just didn't visit an appropriate URL path (example: /documentation/frameworkname). Although if you are truly seeing blank pages with no content at all, it may be worth checking to see if there are any JavaScript or other related errors being reported by your web browser.
One other potential issue is that maybe the version of Xcode you used to create the archive does not contain a recent version of DocC needed to support static hosting. To address that, you could update to the latest beta version of Xcode which would have this newer functionality and then use that to build your documentation for exporting the archive before running the process-archive command.
Also, you may need to also pass the --hosting-base-path argument if you intend to host the static site on a URL that includes a base path, like some GitHub Pages URLs may require (for example you may need to use something like --hosting-base-path /myrepo for a URL that needs to support something like /myrepo/documentation/frameworkname).
Hopefully some part of this information helps with your specific situation! You may also want to check out some recent related documentation for the DocC Swift Package Manager plugin at https://apple.github.io/swift-docc-plugin/documentation/swiftdoccplugin/publishing-to-github-pages
