Additional features, settings, or issues not covered by specific Microsoft Teams categories
I had this issue investingated last week. Here is the response from Microsoft:
I have shared the video with the senior team, and they have confirmed that this is indeed a new update in Microsoft Teams. It was a feature requested on the user feedback page.
This update is being rolled out to all tenants globally, not just to your users.
see link Copying the selected text should only copy selected text, not sender · Community (microsoft.com)
{https://feedbackportal.microsoft.com/feedback/idea/6186a0fe-f402-ef11-a73d-6045bd7e894e}
Additionally, some customers are advocating for this to be an optional feature, and hopefully, that will be implemented as well.
Osahon Ozabor.
Support Engineer - Microsoft Teams.
For Microsoft Customer Support
Working Hours: Monday - Friday 1:00PM – 9:00 PM (UTC)