I used the protocol handler icon to add Proton Mail as my preferred mailto: URI client in Brave. However, mailto: email links on various websites continue to malfunction.
When opened in a new tab, the links would render a completely blank page.
When opened in the same tab, nothing would happen. The location would remain as it was on the page that contains the email link.
Eventually, I stumbled across brave://settings/handlers, diving into the guts of the configuration system. There, I found that my email service, Proton Mail, was present. But strangely not marked as default.
I’m not sure that Web browsers need to support the existence of configurations that include multiple simultaneously registered email services.
I doubt that any user would benefit from a URI handler system that permits a configuration with a positive number of email handlers registered with none of them being the default email handler.
In any case, desktop Brave clients appear to have multiple bugs:
Please automatically set the selected email service as the default, when activating an email protocol handler icon, when there are no other email services registered.
If there were other email services registered at the time a unique one is registered, then prompt the user to confirm which should be the default.