A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Brian Mair
You can refer to AI's answer for the detailed explanation of how sharing and permission inheritance work in SharePoint.
I would just add that based on my research, there is currently no Microsoft documentation or announcement confirming the behavior you observed, specifically a user with Contribute permission now seeing Stop sharing disabled after sharing a file, as a new intentional change. Microsoft's current guidance continues to provide Manage access for managing sharing links and direct access to SharePoint files and folders.
For more information, you can refer to:
Manage sharing and permissions in OneDrive and SharePoint | Microsoft Support
External or guest sharing in OneDrive, SharePoint, and Lists | Microsoft Support
Since you mentioned that this worked differently until very recently, if the behavior can be reproduced with multiple users/files and there have been no changes to the site's permissions or tenant sharing settings, it would be worth opening a support request through the Microsoft 365 admin center. The support team can check the service-side information for the tenant and confirm whether this is related to a recent service change or an unexpected issue.
For further instructions, you can follow this guide: Get support - Microsoft 365 admin | Microsoft Learn.
I hope this information helps.