SUMMARY
Weirdly enough, today, for an unknown reason, I started to have a bug which 
disable some of Krita's functions including modifier key inputs.


STEPS TO REPRODUCE
Unsure. I believe the bug is caused by a certain incompatibilty with some PS features, as it only happens after I open a particular Psd file created from Photoshop CC 2020 v21.1.3.
So what's included in the psd files ? Smart-Objects with a layer style : stroke.

OBSERVED RESULT
After clicking/selecting any layer, the following are disabled :
-Holding CTRL key to color pick, and yet CTRL + Z works
-Holding SHift + Left Mouse/pen click to reduce/increase brush size
-Hodling CTRL + Space to zoom in/out.

EXPECTED RESULT
None of the above issues.

ADDITIONAL NOTE: 
After a certain time as I was writing this, the weird behavior vanished and things went back to normal again. Even after I reopened the same PSD file without changing anything and clicked on a layer again.

SOFTWARE/OS VERSIONS
Windows 10 1909 

ADDITIONAL INFORMATION
Krita

 Version: 4.3.0
 Languages: en_US, en, en_US, en, en_US, en, en_US, en, en_US, en, en_US, en, en_US, en, en_US, en, en_US, en
 Hidpi: true

Qt

  Version (compiled): 5.12.8
  Version (loaded): 5.12.8

OS Information

  Build ABI: x86_64-little_endian-llp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: winnt
  Kernel Version: 10.0.18363
  Pretty Productname: Windows 10 (10.0)
  Product Type: windows
  Product Version: 10

OpenGL Info
 
  Vendor:  "Google Inc." 
  Renderer:  "ANGLE (NVIDIA GeForce GT 640M Direct3D11 vs_5_0 ps_5_0)" 
  Version:  "OpenGL ES 3.0 (ANGLE 2.1.0.57ea533f79a7)" 
  Shading language:  "OpenGL ES GLSL ES 3.00 (ANGLE 2.1.0.57ea533f79a7)" 
  Requested format:  QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::DoubleBuffer, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::CompatibilityProfile) 
  Current format:    QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples 0, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::NoProfile) 
     Version: 3.0
     Supports deprecated functions false 
     is OpenGL ES: true 

QPA OpenGL Detection Info 
  supportsDesktopGL: true 
  supportsAngleD3D11: true 
  isQtPreferAngle: false 

Hardware Information

  GPU Acceleration: angle
  Memory: 12126 Mb
  Number of Cores: 4
  Swap Location: C:/Users/Yed/AppData/Local/Temp

Current Settings

  Current Swap Location: C:/Users/Yed/AppData/Local/Temp
  Current Swap Location writable: true
  Undo Enabled: true
  Undo Stack Limit: 400
  Use OpenGL: true
  Use OpenGL Texture Buffer: true
  Use AMD Vectorization Workaround: false
  Canvas State: OPENGL_SUCCESS
  Autosave Interval: 300
  Use Backup Files: false
  Number of Backups Kept: 1
  Backup File Suffix: ~
  Backup Location: Same Folder as the File
  Backup Location writable: false
  Use Win8 Pointer Input: false
  Use RightMiddleTabletButton Workaround: false
  Levels of Detail Enabled: true
  Use Zip64: false


Display Information
Number of screens: 1
	Screen: 0
		Name: \\.\DISPLAY1
		Depth: 32
		Scale: 1
		Resolution in pixels: 1600x900
		Manufacturer: 
		Model: 
		Refresh Rate: 60