Only Powerpoint templates in Create in Office.com

This is a very common point of confusion for Microsoft 365 administrators, and you've stumbled upon a key difference in how Microsoft handles templates between desktop and web applications.

You are correct. The behavior you're seeing is by design. The PowerShell command you ran is the direct cause.

When you run this command:

Set-SPOTenant -OrganizationAssetsLibraryUrl <URL> -OrganizationAssetsLibraryType OfficeTemplateLibrary

You are telling your entire Microsoft 365 tenant: "From now on, for all web-based Office apps (like create.office.com), ignore the default Microsoft template gallery and only show templates from this specific SharePoint library."

This is why you only see your organization's templates on the web. The web applications are respecting your central configuration.

You can maybe use this workaround to resolve this.

The "Best of Both Worlds"

The create.office.com service needs to be able to read the files in your template library. When permissions are too restrictive, it falls back to showing only what it can guarantee access to, which in a misconfigured state can sometimes result in an empty or limited view. However, the most common reason for seeing only your templates is that the setting is working as intended, but you want to add the Microsoft ones back.

Unfortunately, you cannot simply "add" the Microsoft gallery back. The OrganizationAssetsLibrary setting is designed to be an override, not an addition.

The Real Solution for a Hybrid Approach:

The intended way to have both is to populate your organization's template library with the Microsoft templates you want your users to have.

1. Download the desired Microsoft templates (e.g., a project plan, a pitch deck) from the public Microsoft template gallery or from a machine where they are available in the desktop app.
2. Upload these .potx, .dotx, and .xltx files into your designated SharePoint library (https://tenant.sharepoint.com/sites/sjablonen/OfficeTemplates).
3. Ensure Permissions are Correct: The library must be accessible by the users. The easiest way is to ensure that "Share with Everyone" or at least a broad security group that includes all your users has Read permissions on the site and the library. The create.office.com service acts on behalf of the user, so if the user can't see the file, the service won't show it.

When you do this, users will see your custom templates and the Microsoft templates you've added to the library, all in one place in the web app.

I hope this information helps you with your plans.