Teams tag is mainly focused on the general issue of Microsoft Teams troubleshooting. According to your description, your question is related to Teams Development which is not in our support scope. To better help you solve your problem, please add the Teams Development tag to your post.The following suggestion is just for your reference:
According to our testing, when you use &message=<precanned text>, the text will be displayed to multiple users, which should be a default behavior of Teams.
If you want to avoid this issue, we recommend that you only use https://teams.microsoft.com/l/chat/0/0?users=<user1> and enter the text manually in the chat box.
To fix the problem more quickly, you can send a feedback directly to Microsoft Feedback to add it in future updates.
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.
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