You're opening this as a local file.
Browser extensions like Phantom are blocked on file:// URLs for security reasons.

Serve it over HTTP instead — run this in your terminal:

python -m http.server 8080

Then open http://localhost:8080 in your browser.

Phantom wallet not found.
Make sure the Phantom extension is installed and enabled in your browser.

Or use Demo Mode — pixels are saved locally, transactions are simulated.