Based on our research, there is no way to change user's nickname in Teams. you can send your feedback in Microsoft Teams, and then select Help at the bottom lower-left of Teams and then choose Suggest a feature or Give feedback to tell us what you think.
Meanwhile, to get this feature more quickly, we also recommend you give the feedback in Teams UserVoice and help us make improvements and build new products. Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future. Thanks for your understanding and support!
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.