The expected format of the output configuration values is not currently documented.
From looking at how the completions work, a correct format is like DP-1 or eDP-2.
It would be helpful to document if these are the only the accepted formats, since these values sometimes change.
Sway supports targetting a specific brand/model/serial number with values like " "Some Company ABC123 0x00000000". From a test, it appears Fuzzel doesn't support that style if output ID, but maybe there's another format I'm missing.
This relates some to #130, because if people are going to be able to position Fuzzel, they will also likely want to target the specific monitor it appears on.