I suspect @Sleepy is on the right track here. If you installed youtube-dl through Homebrew, it will not be in /usr/local/bin. The Homebrew people changed the directory for executables on Apple Silicon Macs. It's now /opt/homebrew/bin. To confirm where youtube-dl is, run
which youtube-dl
in Terminal.
If you're a heavy user of Homebrew-installed utilities, you'll need to change several of your macros to reflect their new location. Or you can change Keyboard Maestro's ENV_PATH variable, as described in the article @macdevign_mac linked to.