Right! And maybe yarn needs to be installed globally?
npm i -g yarn
Additionally, some other things to try:
delete your yarn file
in your app directory try d2 app scripts init .
run yarn before using yarn run start (also, sometimes yarn run start works while yarn start doesn’t, I haven’t spent time investigating why, but it does)
@dmaritim were you able to resolve this? I am having the same error using Node v20.9.0 and running the app-platform. I tried to start the playground example app.