Created attachment 131787 [details]
Screenshot of my laptop monitor

The first screenshot was from my desktop, and my laptop doesn't show any of the black borders.

It looks compositing is disabled on your computer. Go to system settings, and make sure that "Enable compositor on startup" is checked in Compositor settings.

If this is indeed a Wayland screenshot, then compositor settings cannot affect the result.

Can you confirm that on both systems the kwin process is actually kwin_wayland instead of kwin_x11? You can use Ctrl+Esc to check the process list.

Oh, right! @techxgames, could you please provide the output of `qdbus org.kde.KWin /KWin supportInformation`?

(In reply to Vlad Zahorodnii from comment #4)
> Oh, right! @techxgames, could you please provide the output of `qdbus
> org.kde.KWin /KWin supportInformation`?

Version
=======
KWin version: 5.19.90
Qt Version: 5.15.0
Qt compile version: 5.15.0
XCB compile version: 1.14

Operation Mode: Xwayland

Build Options
=============
KWIN_BUILD_DECORATIONS: yes
KWIN_BUILD_TABBOX: yes
KWIN_BUILD_ACTIVITIES: yes
HAVE_DRM: yes
HAVE_GBM: yes
HAVE_EGL_STREAMS: yes
HAVE_X11_XCB: yes
HAVE_EPOXY_GLX: yes
HAVE_WAYLAND_EGL: yes

X11
===
Vendor: The X.Org Foundation
Vendor Release: 12008000
Protocol Version/Revision: 11/0
SHAPE: yes; Version: 0x11
RANDR: yes; Version: 0x14
DAMAGE: yes; Version: 0x11
Composite: yes; Version: 0x4
RENDER: yes; Version: 0xb
XFIXES: yes; Version: 0x50
SYNC: yes; Version: 0x31
GLX: yes; Version: 0x0

Decoration
==========
Plugin: org.kde.kwin.aurorae
Theme: __aurorae__svg__Sweet-Mars
Plugin recommends border size: No
Blur: 1
onAllDesktopsAvailable: false
alphaChannelSupported: true
closeOnDoubleClickOnMenu: false
decorationButtonsLeft: 0, 2
decorationButtonsRight: 6, 3, 4, 5
borderSize: 0
gridUnit: 10
font: Noto Sans,10,-1,0,50,0,0,0,0,0,Regular
smallSpacing: 2
largeSpacing: 10

Platform
==========
Name: DRM
Active: true
Atomic Mode Setting: true
Using EGL Streams: false

Options
=======
focusPolicy: 0
xwaylandCrashPolicy: 
xwaylandMaxCrashCount: 3
nextFocusPrefersMouse: false
clickRaise: true
autoRaise: false
autoRaiseInterval: 0
delayFocusInterval: 0
shadeHover: false
shadeHoverInterval: 250
separateScreenFocus: false
placement: 4
focusPolicyIsReasonable: true
borderSnapZone: 10
windowSnapZone: 10
centerSnapZone: 0
snapOnlyWhenOverlapping: false
rollOverDesktops: true
focusStealingPreventionLevel: 1
operationTitlebarDblClick: 5000
operationMaxButtonLeftClick: 5000
operationMaxButtonMiddleClick: 5015
operationMaxButtonRightClick: 5014
commandActiveTitlebar1: 0
commandActiveTitlebar2: 28
commandActiveTitlebar3: 2
commandInactiveTitlebar1: 4
commandInactiveTitlebar2: 28
commandInactiveTitlebar3: 2
commandWindow1: 7
commandWindow2: 8
commandWindow3: 8
commandWindowWheel: 28
commandAll1: 10
commandAll2: 3
commandAll3: 14
keyCmdAllModKey: 16777250
showGeometryTip: false
condensedTitle: false
electricBorderMaximize: true
electricBorderTiling: true
electricBorderCornerRatio: 0.25
borderlessMaximizedWindows: false
killPingTimeout: 5000
hideUtilityWindowsForInactive: true
compositingMode: 1
useCompositing: true
hiddenPreviews: 1
glSmoothScale: 2
xrenderSmoothScale: false
maxFpsInterval: 16666666
refreshRate: 0
vBlankTime: 6000000
glStrictBinding: false
glStrictBindingFollowsDriver: true
glCoreProfile: true
glPreferBufferSwap: 101
glPlatformInterface: 2
windowsBlockCompositing: true

Screen Edges
============
desktopSwitching: false
desktopSwitchingMovingClients: false
cursorPushBackDistance: 1x1
timeThreshold: 150
reActivateThreshold: 350
actionTopLeft: 0
actionTop: 0
actionTopRight: 0
actionRight: 0
actionBottomRight: 0
actionBottom: 0
actionBottomLeft: 0
actionLeft: 0

Screens
=======
Multi-Head: no
Active screen follows mouse:  no
Number of Screens: 1

Screen 0:
---------
Name: HDMI-A-1
Geometry: 0,0,1920x1080
Scale: 1
Refresh Rate: 60


Compositing
===========
Compositing is active
Compositing Type: OpenGL
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) HD Graphics 4400 (HSW GT2)
OpenGL version string: 4.5 (Core Profile) Mesa 20.0.8
OpenGL platform interface: EGL
OpenGL shading language version string: 4.50
Driver: Intel
GPU class: Unknown
OpenGL version: 4.5
GLSL version: 4.50
Mesa version: 20.0.8
Linux kernel version: 5.4
Direct rendering: Requires strict binding: no
GLSL shaders:  yes
Texture NPOT support:  yes
Virtual Machine:  no
OpenGL 2 Shaders are used
Painting blocks for vertical retrace:  no

Loaded Effects:
---------------
zoom
kwin4_effect_login
kwin4_effect_logout
slidingpopups
kwin4_effect_sessionquit
slide
kwin4_effect_windowaperture
screenshot
kwin4_effect_translucency
desktopgrid
colorpicker
kwin4_effect_frozenapp
kwin4_effect_morphingpopups
kwin4_effect_fullscreen
kwin4_effect_fadingpopups
kwin4_effect_maximize
kwin4_effect_fade
kwin4_effect_squash
presentwindows
kwin4_effect_dialogparent
highlightwindow
blur
contrast
startupfeedback
screenedge
kscreen

Currently Active Effects:
-------------------------
blur
contrast

Effect Settings:
----------------
zoom:
zoomFactor: 1.2
mousePointer: 0
mouseTracking: 0
focusTrackingEnabled: false
textCaretTrackingEnabled: false
focusDelay: 350
moveFactor: 20
targetZoom: 1

kwin4_effect_login:
pluginId: kwin4_effect_login
isActiveFullScreenEffect: false

kwin4_effect_logout:
pluginId: kwin4_effect_logout
isActiveFullScreenEffect: false

slidingpopups:
slideInDuration: 150
slideOutDuration: 250

kwin4_effect_sessionquit:
pluginId: kwin4_effect_sessionquit
isActiveFullScreenEffect: false

slide:
duration: 500
horizontalGap: 45
verticalGap: 20
slideDocks: false
slideBackground: true

kwin4_effect_windowaperture:
pluginId: kwin4_effect_windowaperture
isActiveFullScreenEffect: false

screenshot:

kwin4_effect_translucency:
pluginId: kwin4_effect_translucency
isActiveFullScreenEffect: false

desktopgrid:
zoomDuration: 300
border: 10
desktopNameAlignment: 0
layoutMode: 0
customLayoutRows: 2
usePresentWindows: true

colorpicker:

kwin4_effect_frozenapp:
pluginId: kwin4_effect_frozenapp
isActiveFullScreenEffect: false

kwin4_effect_morphingpopups:
pluginId: kwin4_effect_morphingpopups
isActiveFullScreenEffect: false

kwin4_effect_fullscreen:
pluginId: kwin4_effect_fullscreen
isActiveFullScreenEffect: false

kwin4_effect_fadingpopups:
pluginId: kwin4_effect_fadingpopups
isActiveFullScreenEffect: false

kwin4_effect_maximize:
pluginId: kwin4_effect_maximize
isActiveFullScreenEffect: false

kwin4_effect_fade:
pluginId: kwin4_effect_fade
isActiveFullScreenEffect: false

kwin4_effect_squash:
pluginId: kwin4_effect_squash
isActiveFullScreenEffect: false

presentwindows:
layoutMode: 0
showCaptions: true
showIcons: true
doNotCloseWindows: false
ignoreMinimized: false
accuracy: 20
fillGaps: true
fadeDuration: 150
showPanel: false
leftButtonWindow: 1
rightButtonWindow: 2
middleButtonWindow: 0
leftButtonDesktop: 2
middleButtonDesktop: 0
rightButtonDesktop: 0

kwin4_effect_dialogparent:
pluginId: kwin4_effect_dialogparent
isActiveFullScreenEffect: false

highlightwindow:

blur:

contrast:

startupfeedback:
type: 1

screenedge:

kscreen:

Hmm, borders are okay on my machine. Can you reproduce this bug with other aurorae decorations?

(In reply to Vlad Zahorodnii from comment #6)
> Hmm, borders are okay on my machine. Can you reproduce this bug with other
> aurorae decorations?

OH! That's why it was having issues.

So, was it a bug in the decoration theme (Sweet-Mars) that you were using?

This bug was reported against an outdated version of KWin. We have made many changes since the. 
If the issue persists in newer versions can you reopen the bug report updating the version number.