STEPS TO REPRODUCE
0. Open System Settings, navigate to Display and Monitor - Display Configuration.
1. Change display resolution from 2560x1440 144 Hz to 1280x720 60 Hz and apply changes.
2. Set display resolution back to 2560x1440.
3. See refresh rate dropdown showing 144 Hz.
4. Apply the changes.

OBSERVED RESULT
Display runs at 60 Hz.

EXPECTED RESULT
Display to run at 144 Hz. Or refresh rate dropdown show 60 Hz.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.10
Kernel Version: 6.3.9-arch1-1 (64-bit)
Graphics Platform: X11

ADDITIONAL INFORMATION
Xrandr output:
Screen 0: minimum 8 x 8, current 2560 x 1440, maximum 32767 x 32767
DP-2 connected primary 2560x1440+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440    143.97 + 120.00    99.95    59.95* 
   1920x1080     74.91    60.00    59.94    50.00  
   1680x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00    59.94    50.00  
   1152x864      59.96  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x480       59.94  
   640x480       75.00    59.94    59.93     

After step 3, if I open the refresh rate dropdown (which says 144 Hz), and select 144 Hz again, then after applying the changes, the display runs at expected 144 Hz.

Or after step 4, when changes were applied but screen is still running at 1440p 60 Hz, if I reselect the dropdown, Apply button lights up, which after clicking, applies the expected 144 Hz.