Both bucket AND file in a single input for backup destination - how to?

Every new backup does always override the old one, so I’d like to configure a path with strftime time substitution. But it is not clear how do I specify BOTH bucket AND path in a single input?

It works find if I specify bucket only. But how do I specify the path in the same input?

Operating system: Ubuntu
OS version: 20.04


P.S. There are some useful topics that I would like to follow up by adding an updates / asking for clarification, but all topics are closed after 2 months of inactivity.