I have the same problem, I was about to create a new topic, and will if it’s not the same context.
Brand new project from JUCE, even code signing added, AUv3 never shows up anywhere. Tried it on M1 or an old MacBook Pro.
Have you run the standalone version of the application? This seems to be required to register the plugin.
Then, in a Terminal (not iTerm, must be the built-in Terminal.app) reset the plugin cache by running
killall -9 AudioComponentRegistrar
Alternatively, if you’re running the very latest Logic Pro you can go to the Plug-In Manager window and click the “full plugin reset” button.
Now, when you run auval -a from a Terminal, your AUv3 should show up in the list. You can then verify it with auval -v <plugin identifier codes> to see whether it can actually be loaded and used correctly.