There are several ways to create an online class. In the article How do I create an online lesson in Teams? you can read more about this.
This article explains how to track student attendance afterwards. The instructions are provided for each method of creating an online class.
Online lesson created in Teams
When you have created an online class from Teams, you can find the class in your Teams calendar. To check attendance, go to the chat of this meeting. Click on the meeting and then on Chat.
At the top, you will see several tabs, including Attendance. When you click on this, you can view various information, including which students were present. You can also download an export by clicking the Download button.
Online lesson created in Brightspace
To track attendance for an online class created from Brightspace, you must have used the chat.
If you have created an online class from Brightspace, you can also track attendance in the chat. To do this, go to the chat in Teams. Then find the chat for the online class. Click on Attendance, and you will see the same overview as with the previous method.
Online class created in the Teams environment from Brightspace.
If you have created an online class in the Teams environment, you can track attendance in the same way as described here: Online lesson created in Teams