TLDR: Please install VS Code extension Even Betterer TOML (Release Fork) and deactivate the "Even Better TOML" extension.

Longer Answer:

"Even Better TOML" isn't updated since 2023-07-15, because an CI token is expired and the only maintainer with access is not available anymore: see discussion on GitHub.

Therefore, a release fork was created and published as Even Betterer TOML (Release Fork).

In each release of the extension, all schemas from the JSON schema store are included. The schema store has support now for PEP 621 compliant pyproject.toml files for a while now. In the lastest update of the VS Code extension, the newest schema is included and the error message will disappear.