Here are some free electronic whiteboards to use in teaching and research online
https://app.ziteboard.com/ (need to invite people by their email to allow them to draw)
https://www.invisionapp.com/ (students need to log in to be able to draw)
Why use a separate e-whiteboard? The whiteboards in Teams and Zoom are a bit clunky.
Feel free to suggest more whiteboards to me and I'll add them if I like them.