Created attachment 137575 [details]
Screenshot showing just the merged output is blurry/fuzzy.

SUMMARY
In case this impacts anything, I have 2 4k Hi-DPI monitors connected to my laptop through a TB3 dock (the laptop monitor itself is also 4k Hi-DPI). The merge output window has blurry text whereas A/B/C windows are crisp. This applies in 2-way & 3-way diffs.

STEPS TO REPRODUCE
1. kdiff3 -m 1.txt 2.txt 3.txt

OBSERVED RESULT
Merged output is blurry. Additionally spaces are represented as dots (not sure if the latter is intended - I had thought so but I also haven't found any config option to turn it off).

EXPECTED RESULT
Text in merged output is as crisp as it is in the original content views.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kernel 5.10.28-1LTS
(available in About System)
KDE Plasma Version: 5.21.4
KDE Frameworks Version:  5.80.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
GPU: Intel CometLake UHD Graphics & Quadro T2000. Both Intel & Nvidia (under Prime) exhibit this issue.
Display global scale: 200%
Monitors: 2 external 27" @ 3840x2160, laptop @ 3840 x 2400.

PLASMA_USE_QT_SCALING=1 doesn't impact anything.