OK, I am using PureOS with Wayland since >3 years, and I definitely used Zoom. I remember having experienced some problems with screen sharing initially, but thought that had gone away. Now I also get the message that my OS is not supported.
So it seems that Zoom is simply checking the names in /etc/os-release - could it be that previously (e.g. in the “Rolling-Release” days) it did say something different in /etc/os-release, which made Zoom happier?
I can confirm that editing /etc/os-release makes the blocking message go away, and it says that I can share the desktop or the whiteboard. Desktop sharing worked. I can not choose individual windows, but that may be a feature which is not available in the basic account. However, while I could see annotations drawn on the shared desktop from the remote participant, he could not see my annotations. Could that be a problem/feature of wayland?
I am using Zoom version 3.5.392530.0421, which is the current Ubuntu 14.04+ version on the ZOOM Download Center. It seems that different versions behave differently (it is interesting that the Debian version number seems to be 3.0xxx).