Installed: ArcGIS Field Maps 20.4.0, on Portal 10.8.1, and the Resources link points to missing documentation in the filesystem. I read, here, that the documentation should be pointing to the web, but after installing I found the help documentation is pointing locally, and is missing.
I should be able to redirect to the web help to workaround the issue, but I'd rather have the resources locally.
This is a known issue that is not planned to be addressed for the 10.8.1 setups. The on-prem help was not included with the setup for some reason. It is available in the Enterprise 10.9+ versions of Field Maps.