I think this is mostly a command line pain where everything is on one line and needs hint on spaces.
GUI entry is already broken up enough that Duplicati doesn’t need that help. But there’s a style point:
In this case, the displayed quotes point you to the value inside the quotes, not the quotes themselves.
The value inside quotes means either use graphical elements to enter, or use three dot “Edit as text”:
(and note that the quotes there mean the value inside the quotes, not to expect it shown on the page)
--compression-extension-file=C:\Program Files\Duplicati 2\default_compressed_extensions.txt
Entering that first option in Command Prompt would need the value in double quotes to avoid space break.
Was this the misunderstanding? I suppose we could omit quotes, but it might be considered bad style.
Seeing nothing might also make people wonder. What’s the best way to mean literally an empty string?