People sometimes works with multiple database files (eg. some of them are shared with other people), albeit often having a main one which contains the master password for the other databases.

It would be desirable to open them directly from within keepassxc. Currently there doesn't seem to be an option to do so.
I propose that if the url starts with kdbx://, it is captured internally¹ and the rest of the url is treate as a filename opened by the current instance using the password field as master password.

Then, opening such database would be a matter of using the Open URL action over the entry.

¹ This could all be handled externally, but then the password would not be available or it would have to be passed in a less-secure way.