Document libraries - Force users to upload content via the new Forms method only

Microsoft’s new Forms‑based upload experience for document libraries is designed as an additional way to collect files with metadata, not as a replacement for the classic Upload button.

AFAIK: As of now, Microsoft has not announced any plan to disable or replace the standard Upload button. The classic Upload button remains a core, non‑removable part of the document library UI.

Although you cannot disable Upload using out‑of‑the‑box settings, you can hide it using JSON command bar customization

This is the only supported workaround. You can apply JSON formatting to a library view to hide specific built‑in commands.

Example JSON to hide New + Upload:

{
    "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",
    "commandBarProps": {
      "commands": [
        {
          "key": "newComposite",
          "hide": true
        },
        {
          "key": "UploadCommand",
          "hide": true
        }
      ]
    }
  }

Important notes:

• This must be applied per view
• If you want the entire library locked down, apply it to all views
• Users with Manage Lists permission can still edit/remove the JSON
• This does not remove the Upload capability from APIs or sync clients
• If a user has the ability to edit list settings or create a new view, they can still see the New button in their personal view or any new view where the JSON formatting is not applied.

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