The textDocumentNotebook api proposal is currently not on track for finalization. See #102091 (comment) for details on this

As an workaround, today you can achieve the same functionality with:

vscode.workspace.notebookDocuments.find(notebook => notebook.getCells().some(cell => cell.document === myTextDocument))

We plan to remove the TextDocument.notebook property once all consumers have moved off of it:

• LiveShare @alyssajotice @fubaduba
• Dot net interactive @brettfo, @colombod
• Copilot (and copilot nightly) @Krzysztof-Cieslak (let me know the correct owner if I got this wrong)
• Remove usage of textDocumentNotebook proposed API vscode-jupyter#9679

If you are on this list, please look into migrating off of this api and let us know if you run into any issues with the migration