Thank you! npm run dev was the key (i ran npm run build and npm run plugin:pack).
That's exactly what I did, since the instructions didn't make sense. And it seemed to work.
➜ Flexbar-TouchbarEmulator git:(main) ✗ node -v
v24.6.0
In my case I had to change line 7 (not 6) of /opt/homebrew/lib/node_modules/@eniac/flexcli/src/commands/pack.js
Did you create this? It's beautiful! And it fits perfect next to the audio spectrum thing.
I'm now running it and some generic shortcuts on the main page, and one of the icons start a page with BTT and AquaTouch. Now I just wish I could combine Flexbar plugins with BTT stuff in the same screen, instead of having to switch back and forth.