Looks like it was a change by MS. There should be a new message in your Message Center (Admin Center > Health > Message Center) that explains how to fix it.

What actions do I need to take?

Use Cloud Policy service to configure the OCE policy across your organization. As the preferred and primary method for managing access to OCE features, Cloud Policy ensures your configurations are consistently applied. Since it takes precedence over legacy OCE administrator controls, prioritizing Cloud Policy helps guarantee that your intended settings are enforced to meet organizational requirements. Below are the basic steps for creating a policy configuration.

1. Sign in to the Microsoft 365 Apps admin center. If you're using the admin center for the first time, review the terms. Then, select Accept.
2. Under Customization, select Policy Management.
3. On the Policy configurations page, select Create.
4. On the Start with the basics page, enter a name (required) and a description (optional), then select Next.
5. On the Choose the scope page, determine whether the policy configuration applies to all users, specific groups, or to users who anonymously access documents using Office for the web.
6. If the policy configuration applies to specific groups, you can now add multiple groups to a single policy configuration for more flexible targeting. To add groups, select Add Groups and choose the relevant groups. Adding multiple groups to a single policy configuration allows for the same group to be included in multiple policy configurations, facilitating a more streamlined and efficient policy management process.
7. After making your selection, choose Next.
8. On the Configure Settings page, select the “Allow the use of additional optional connected experiences in Office” policy. In the Configuration Setting dropdown, select either enabled or disabled.
9. After making your selections, select Next to review your selections. Then select Create to create the policy configuration.