I don't know what else to say. I work with people who put on live shows for 20,000+, they use PCs and Macs to drive the display WITHOUT Decklink or similar, and they would be upset if there was a persistent orange dot on the screen. If you want to split hairs about whether or not that makes the new macOS "unusable" in these situations, then fine, but in the environment I'm familiar with it would not be tolerated. They would replace the Mac device with a PC which doesn't have this issue because they would deem it unusable, even though it can technically still display images on a screen.

And despite your repeated comments on this article, it IS possible to configure a PC to not show any notifications for use in a live show, between a combination of changing OS settings, closing unneeded programs, and using the fullscreen APIs of the OS. This is something that can be done ahead of time and tested. I've written software that shows fullscreen on secondary displays on large projectors for presentation-like purposes and I have never had an OS notification pop up over the fullscreen software on a secondary display, even on other people's machines where they didn't take care to shut down programs and turn off notifications. Other commenters here seem to have similar experiences.