SUMMARY
CapsLock behavior is not decided by the current selected layout but by the layout that is first in the list in System Settings.
It looks like these bugs from the descriptions: https://bugs.kde.org/show_bug.cgi?id=171632 and https://bugs.kde.org/show_bug.cgi?id=360145

STEPS TO REPRODUCE
1. Add two layouts in System Settings: English (US) and English (US) (Colemak variant).
2. Put the colemak or the non-colemak variant first of the list of layouts.
3. Hit CapsLock, switch layouts and hit again.

OBSERVED RESULT
1. if colemak variant is first of the list of layouts:
  - if colemak is selected: Backspace as expected.
  - if non-colemak is selected: Backspace -> UNEXPECTED
2. if non-colemak variant is first of the list of layouts:
  - if non-colemak is selected: CapsLock as expected.
  - if colemak is selected: CapsLock AND Backspace (delete previous character and lock capital letters)

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.2.3
KDE Frameworks Version: 6.8.0
Qt Version: 6.8.0
Kernel Version: 6.6.59-1-lts (64-bit)
Graphics Platform: Wayland