venv/share/jupyter/lab/schemas/@jupyter-notebook/notebook-extension/checkpoints.json

{
  "title": "Notebook checkpoint indicator",
  "description": "Notebook checkpoint indicator",
  "jupyter.lab.toolbars": {
    "TopBar": [{ "name": "checkpoint", "rank": 20 }]
  },
  "properties": {},
  "additionalProperties": false,
  "type": "object"
}