Controlling data sharing, visibility, and access permissions within Microsoft Teams for Education
Hi Betty,
Based on the description, it seems that the issue happen when you are using Teams web client (https://teams.microsoft.com) and open multiple tabs to access other website as well. However, there is no setting to turn off this feature.
Moreover, you use download and use Teams app on Chromebook as a workaround. You may refer to the article under "How to install Office apps on a Chromebook" and click on Teams links to download the app. See How to install and run Microsoft Office on a Chromebook
Your patience and cooperation will be highly appreciated. Have a nice day and stay safe!
Best regards,
Shyamal