When I Right-lick a weird blank window appears "MixedDpiMenuFixer". I thought it had to do with my AMD installation. So I completely uninstalled the AMD programs and then installed just the driver with Windows Update. My OS is Windows 10 Pro 64 bit fully updated. This doesn't happen in Windows File Explorer.
Those windows should be hidden, so for one to appear means there's probably a bug in something else on your system. My guess would be whichever tool you're using to get non-standard window borders.
You can set Preferences / Miscellaneous / Advanced: [Troubleshooting] mixed_dpi_mitigations to False to prevent the hidden window being created at all. But you may then see other problems (usually context menus that are not scaled properly) due to bugs in Windows itself when using multiple screens at different DPIs. The hidden window is created to work around those bugs when mixed DPI is detected.
(High DPI is OK, as are multiple monitors. But multiple monitors running at different DPIs to each other, or changing DPIs without rebooting afterwards, will put Windows into a mode which is riddled with bugs.)
Thanks for the quick reply. Here are my settings:
All Settings>Expand>Project>"Extend". The extension monitor is my 42" tv set. Now in Display Settings or respectively in AMD Settings Monitor 2 (TV set) is set to 150% (Recommended) 1920x1080 (Recommended, 3D). Could this be the problem? Would "Duplicate" instead of "Extend" be the right choice?
The scale percentage (175% on monitor 2, but the screenshot doesn't show what monitor 1 is) should be the same for both displays, ideally.
Monitor 1 is my main monitor set at 100%. Now, I reset monitor 2 (tv set) to 100% and the "bug" never showed up again. So, you're right OF COURSE! BOTH monitors should be set to the same scale percentage. Thanks a lot for your constructive help! Greetings from Greece!