The documentation is purposefully deceiving. It makes you believe, in good faith, that disabling telemetry is per project when in reality it is per machine.
I just tried it myself on a brand new Next project:
$ npx create-next-app@latest
...
$ npx next telemetry disable
Next.js' telemetry collection is already disabled.
Status: Disabled
You have opted-out of Next.js' anonymous telemetry program.
No data will be collected from your machine.
Learn more: https://nextjs.org/telemetry
Note the part that says "from your machine".An issue was crated about it but they just closed without responding: https://github.com/vercel/next.js/issues/31360
THIS
Sure.
1. Last paragraph of that link you posted
2. https://github.com/vercel/next.js/issues/8851
3.https://github.com/vercel/next.js/issues/10713
4. Many similar discussions to this one here on hackernews.
[0] https://nextjs.org/telemetry