This isn’t a server side issue but a client configuration issue.
You’re referring to the UI URL in maven instead of the URL to be used to download the artifacts.
The URL you should use should be something like this: Https://server:port/repository/your-repo-name.
I’m not too strong in java and maven, but for apt repositories it helped to remove this checkbox.
Especially with keys with a key extension. They are always considered binary by the nexus, but often they are textual. Because of what, instead of a file, an html page was returned with a warning about the wrong content type
Turns out it was a combination of wrong URL syntax and invalid authentication setup. Since Maven couldn’t authenticate, Nexus was attempting to return an HTML page with error information; but all I got was an HTML file with JS references and no real text.