List my app in "default web browser" list in Big Sur

Hi.

I'm developing a macOS app called Finicky (https://github.com/johnste/finicky) that acts as a web browser. Up until and including macOS Catalina it was visible in the list of browsers you could set as the default one, but after upgrading to Big Sur it's missing from the list.

The plist includes CFBundleURLTypes for both http and https so I'm not sure what changed.

How can I add it back to the list of options for default web browsers?