SUMMARY

There is a 1px gap at the bottom of the built-in 2K (2560x1440@60) laptop screen, below a 64px bottom Plasma panel. The gap is gone if the panel is expanded to 66px, but is back if reverted to 64px.


STEPS TO REPRODUCE
0.a. Set X11 global scaling to 150%, reboot.
0.b. Add `export PLASMA_USE_QT_SCALING=1` to your session file (~/.zprofile in my case with zsh)
1. Set screen to 2K (2560x1440) mode.
2. Add bottom panel.
3. Set panel's height to 64px.

OBSERVED RESULT
A 1px gap between the panel and the bottom edge of the screen. The gap is visible, and does not handle mouse input (clicks get passed through).

EXPECTED RESULT
There should be no gap.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Version: git-master everything
Qt Version: 5.15.7
Kernel Version: 6.0.12-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-8565U CPU @ 1.80GHz
Memory: 15.3 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620
Manufacturer: LENOVO
Product Name: 20QD003CRT
System Version: ThinkPad X1 Carbon 7th

ADDITIONAL INFORMATION