SUMMARY The arrangement-specific scaling setting is actually global. STEPS TO REPRODUCE 1. Turn on laptop without an external screen. 2. Go to Sytem Settings -> Display and Monitor -> Save display's properties -> select "For only this specific display arrangement". 3. Change scaling to something non-default, such as 125%. 4. Connect external screen. 5. Optionally, restart the computer with the laptop lid closed so that it starts right away with the external screen on. 6. Go to the configuration for the external screen. OBSERVED RESULT It has the same scaling that I had configured for the laptop screen and which was "only for that specific arrangement". EXPECTED RESULT Should have the scaling that I last set for this screen. SOFTWARE/OS VERSIONS Operating System: Debian GNU/Linux 12 KDE Plasma Version: 5.27.2 KDE Frameworks Version: 5.103.0 Qt Version: 5.15.8 Kernel Version: 6.1.0-5-amd64 (64-bit) Graphics Platform: X11 Processors: 20 × 12th Gen Intel® Core™ i7-12700H Memory: 62.6 GiB of RAM Graphics Processor: Mesa Intel® Graphics Manufacturer: SLIMBOOK Product Name: Executive ADDITIONAL INFORMATION
This setting has been removed for Plasma 6, so the bug is no longer capable of happening. :)