I have had the same problem as well. My Surface Pro 7 (purchased last in Nov. 2020) works great, including using Zoom for video conferencing. However, when screen sharing with touchpad applications such as OneNote, DrawboardPDF and Whiteboard, things go down go downhill quickly. I teach college physics courses with Zoom, which are handwriting intensive with OneNote (or similar application) and I experience similar performance issues as others have described, including severe lag, screen momentarily going black, program restarting, SP7 rebooting, etc. It has been especially bad using OneNote which is my preference. Of course, I've tried multiple versions of OneNote (both the 2016 and Win10 versions), as well as various online solutions such as disabling hardware acceleration, etc. to no avail.
To add insult to injury, I recently purchased a Lenovo Flex 5 Ryzen 2-in-1 (16GB/512GB). It was on sale at Costco so I couldn't resist. The Flex5 has more or less the same specs as my SP7, a different microprocessor of course, but it streams my Zoom sessions while screen sharing OneNote just fine. This device cost me less than half the price of I paid for the SP7 yet does everything I purchased the SP7 to do. Grr. My only complaints with the Flex5 are the stylus/touchpad isn't as nice as the SP7, and the screen brightness is too dim for my liking even on the brightest setting. I'm still adjusting to the new device but at least it works great. Microsoft needs to address this problem and make things right. Or, the company is going to lose the support of a lot of educators in the future.