Did you include the 2nd line of text with the derivation path? If so, what derivation path did you use?
Note that the one in the example (m/23/23'/33) is NOT a "standard" Bitcoin derivation path (which would tend to be something like m/44'/0'/0' or m/49'/0'/0' or m/84'/0'/0' etc)
However the Cold Card will not allow me to specify which address to use sign the message and the one it's pulling for me by default is not the one I want. Also since I'm new to Cold Card and what I would consider a novice with Electrum I went ahead and signed the text message anyway with the address it defaulted to. I noticed that this address was one that wasn't listed in the Electrum view of my Cold Card wallet and furthermore I wasn't sure how to load it into Electrum.
It says in the coldcard docs linked above that it will default to the master key of "m" if a valid derivation path is not supplied. This would probably explain why it doesn't show in Electrum... it probably wouldn't show in any wallet.
The key subpath is optional and specifies a path from master key, such as m/48'/0'/0' or similar. If not provided, the master key (m) is used as a default.