tldr: Make sure Rosetta is installed, as KMLink still runs Intel binaries. That was the failure mode in my case.
(Also posted this to New Stream Deck – KM Link Not Working - #15 by Chetan_Madhani)
This seems to be a thread that consolidates a lot of good information. I recently moved to a new Mac, macOS Sequoia installed, and KMLink stopped working.
My old KMLink shortcuts were still programmed into the Stream Deck software, but the Macro field was greyed out (as above) and the arrow / spinner was spinning.
When adding new KMLink shortcuts to the Stream Deck, I was unable to see or select anything in the Macro field, and the spinner was just spinning.
Pressing an old KMLink enabled macro just resulted in the yellow warning triangle with the exclamation mark.
Turns out, KMLink couldn't run without Rosetta installed, and it doesn't prompt an "Install Rosetta" dialog for... reasons. Instead, run:
/usr/sbin/softwareupdate --install-rosetta
in the Terminal.
Hope that works!