Yes, you can do that. You have one manual step involved as this is not a frequent ask.

Follow our setup document to Authorize 'Tab SSO' -

https://docs.servicenow.com/bundle/rome-employee-service-management/page/product/sn-teams/task/authorize-multi-tenant-apps.html .

Follow - https://docs.servicenow.com/bundle/rome-employee-service-management/page/product/sn-teams/task/download-manifest-file.html with enable Tabs.

In step 2, open the content of the zip, you will find a manifest.json file. In it remove the lines in screenshot in attachment and save the file. zip back by selecting the 3 files. Do note that zipping the folder instead of files, results in error on Microsoft side.

Your Teams App should now be set with the Tab and not the chat. If you wish to still see VA chat in the Employee Centre portal check this page - https://docs.servicenow.com/bundle/rome-employee-service-management/page/product/sn-teams/task/disable-chat-button-teams-custom-portal.html . We ship a style sheet to hide the chat in Portal when used in context of Teams. Remove the style pointed there.