Thanks! Can you document how it is used?

I tried "options_disabledMediaRanges": ["application/pdf"] but yet instead of the raw PDF the data browser is served. My config is:

{
      "comment": "Serve the Mashlib Data Browser as default container representation",
      "@id": "urn:solid-server:default:DefaultUiConverter",
      "@type": "ConstantConverter",
      "filePath": "./node_modules/mashlib/dist/databrowser.html",
      "contentType": "text/html",
      "options_minQuality": 1,
      "options_container": true,
      "options_document": true,
      "options_disabledMediaRanges": ["application/pdf"]
}

That looks good! You're running v1.1.0?
Perhaps post a debug log, then we can check.

Yes I am running v1.1.0.

Turns out the option works fine, but the problem lies in ACL / authentication. If I grant public access to the PDF I can load it in the browser, but if the access is restricted it serves the data browser.

Super, that was the intended behavior, because Databrowser has a UI that helps you sign in.

Not sure if the behaviour is really intended like that, because even after signing in via UI I am getting served the HTML, not the raw PDF. I guess this is because the browser's get request ist getting a 401 still, since it does not include an Authorization header and plain cookies are not supported? (I tried with a data browser that is using @inrupt/solid-client-authn-browser, so this is not an issue with old-style auth)

I guess this is because the browser's get request ist getting a 401 still, since it does not include an Authorization header and plain cookies are not supported?

Yes, Databrowser is currently not compatible with the Solid specification; there is an active branch that is adding support, expected in the next couple of weeks.