I am not sure if it is an issue with the mac software or something glitch-y caused by Affinity Photo. I have contacted Apple as well about the issue. But when I open a file in Affinity Photo app and my screen is on full brightness, the screen changes to a black with lined colors to slightly outline the app and image. I have attached a screenshot. Hard to explain. At first I thought it was an overall issue with the mac, but it seems to only happen when I have Affinity Photo open and have additionally opened a file. It was merely by accident that I discovered it was a brightness thing. I unplugged my mac to go in a low light room to take a picture of the screen. When I unplugged it, the issue went away, so I wasn’t going to be able to take a photo of it. Then it hit me that it might be brightness related. I have my mac set to dim screen when unplugged. so i increased the brightness back to 100% and the issue returned. Turned it down just one level, gone. did it a few times to be sure. Then, oddly, it changed when I returned to mess with Photo. Now, it happens no matter the brightness level. If I quit Affinity Photo, issue goes away as well. Doesn't happen in any other app on my mac.