Can you attach logs from when the issue occurs?
I was also able to reproduce this issue with Minecraft 1.16.2 and 1.16.3. I've tested on two new MacBooks Pro running OSX Catalina and one older MacBook.
During my investigation I've found that that these issues are caused by the LWJGL library (we could add lwjgl label to the ticket).
The "launcher_log.txt" and "launcher_cef_log.txt" files in the "/Users/XXX/Library/Application Support/minecraft/" directory.