I didn't read through all the comments, so this may have been mentioned already. This isn't broken, this is decision put in place by the Teams group.
https://admin.microsoft.com/#/MessageCenter/:/messages/MC878422
Summary
Teams has removed timestamps and author names from copied messages to reduce clutter. Users who need detailed message transfer should use the Forward feature or Teams Export API. This change is already in effect, and organizations may need to update training materials accordingly.
Many users have voiced frustrations over copying messages in Teams, particularly the inclusion of metadata like names and timestamps. Customer feedback has been clear, signaling that this feature was adding more noise than value to user workflow.