Thanks for the hint.
Unfortunately, this project cannot open Obsidian vaults in arbitrary locations. The reason seems to be that Obsidian keeps track of existing vaults in .config/obsidian/obsidian.json, and only vaults that exist in this file can be opened via URI. (See "obs ." to open the current directory · Issue #23 · Yakitrak/obsidian-cli · GitHub)
The problem is that Obsidian checks at every startup whether the locations of the vaults in .config/obsidian/obsidian.json still exist. But if a vault lives on a USB drive or remote location, then it might not be accessible every time Obsidian is started and gets removed. Hence, it is not registered in the obsidian.json anymore.
The question is whether this behavior can be modified.