Disabling hardware acceleration for Night Shift
Since the artifacts disappear whenever an overlay appears, I solved the issue by creating an app that displays a persistent, invisible overlay:


Created a new macOS Cocoa App in Xcode.
Edited the window properties in MainMenu.xib, in the attributes inspector, and unchecked "Title Bar", "Shadow", "Close", "Minimize" and "Resize", then in the size inspector I set content size width and height to 1, and initial position x and y to 0.
Edited Info.plist and added a new property "Application is agent (UIElement)" set to YES.
Edited AppDelegate.swift and changed applicationDidFinishLaunching to:


window.isOpaque = false
window.alphaValue = 0
window.ignoresMouseEvents = true
window.level = .floating
window.collectionBehavior = [.canJoinAllSpaces, .transient]

Compiled the app for production with Product  Archive  Distribute App  Copy App.


Now, whenever I want to watch full-screen videos with Night Shift turned on, I can start the application and there won't be any further artifacts. I can then close it from Activity Monitor. Another option would be to have it run at startup (System Preferences  Users &amp; Groups  Login Items).