When I entered other tty terminals via ctrl+fn+Fn, when I switched back to the tty1 graphical desktop, the graphical desktop started to freeze. Try to use kquitapp5 plasmashell; kstart5 plasmashell to restart the desktop environment, the lag problem still cannot be solved.
Can someone help me? That would be greatly appreciated.

The following are my screen parameters and graphics card environment.

Screen 0: minimum 8 x 8, current 5760 x 2160, maximum 32767 x 32767
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-0 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 600mm x 340mm
3840x2160 60.00*+ 59.94 50.00 30.00 29.97 25.00 23.98
2560x1440 59.95
1920x1080 60.00 59.94 50.00 29.97 23.98
1600x900 60.00
1280x1024 60.02
1280x800 59.81
1280x720 60.00 59.94
1152x864 60.00
1024x768 60.00
800x600 60.32
720x576 50.00
720x480 59.94
640x480 59.94 59.93
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
eDP-1-1 connected 1920x1080+3840+688 (normal left inverted right x axis y axis) 344mm x 194mm
1920x1080 60.03*+ 60.01 59.97 59.96 59.93
1680x1050 59.95 59.88
1400x1050 59.98
1600x900 59.99 59.94 59.95 59.82
1280x1024 60.02
1400x900 59.96 59.88
1280x960 60.00
1440x810 60.00 59.97
1368x768 59.88 59.85
1280x800 59.99 59.97 59.81 59.91
1280x720 60.00 59.99 59.86 59.74
1024x768 60.04 60.00
960x720 60.00
928x696 60.05
896x672 60.01
1024x576 59.95 59.96 59.90 59.82
960x600 59.93 60.00
960x540 59.96 59.99 59.63 59.82
800x600 60.00 60.32 56.25
840x525 60.01 59.88
864x486 59.92 59.57
700x525 59.98
800x450 59.95 59.82
640x512 60.02
700x450 59.96 59.88
640x480 60.00 59.94
720x405 59.51 58.99
684x384 59.88 59.85
640x400 59.88 59.98
640x360 59.86 59.83 59.84 59.32
512x384 60.00
512x288 60.00 59.92
480x270 59.63 59.82
400x300 60.32 56.34
432x243 59.92 59.57
320x240 60.05
360x202 59.51 59.13
320x180 59.84 59.32
1280x1024 (0x1cf) 108.000MHz +HSync +VSync
h: width 1280 start 1328 end 1440 total 1688 skew 0 clock 63.98KHz
v: height 1024 start 1025 end 1028 total 1066 clock 60.02Hz
1280x800 (0x1d0) 83.500MHz -HSync +VSync
h: width 1280 start 1352 end 1480 total 1680 skew 0 clock 49.70KHz
v: height 800 start 803 end 809 total 831 clock 59.81Hz
1024x768 (0x1d4) 65.000MHz -HSync -VSync
h: width 1024 start 1048 end 1184 total 1344 skew 0 clock 48.36KHz
v: height 768 start 771 end 777 total 806 clock 60.00Hz
800x600 (0x1d5) 40.000MHz +HSync +VSync
h: width 800 start 840 end 968 total 1056 skew 0 clock 37.88KHz
v: height 600 start 601 end 605 total 628 clock 60.32Hz
640x480 (0x1d8) 25.175MHz -HSync -VSync
h: width 640 start 656 end 752 total 800 skew 0 clock 31.47KHz
v: height 480 start 490 end 492 total 525 clock 59.94Hz
Thu Sep 2 17:11:53 2021
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 390.144 Driver Version: 390.144 |
|-------------------------------+----------------------+----------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
|===============================+======================+======================|
| 0 GeForce GTX 1060 Off | 00000000:01:00.0 On | N/A |
| N/A 46C P8 6W / N/A | 2028MiB / 6078MiB | 0% Default |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| 0 543 G /usr/lib/Xorg 825MiB |
| 0 1289 G /usr/bin/kwin_x11 127MiB |
| 0 1333 G /usr/bin/plasmashell 118MiB |
| 0 82335 G /usr/bin/systemsettings5 127MiB |
| 0 90480 G ...AAgAAAAAAAAACAAAAAAAAAA= --shared-files 46MiB |
| 0 94865 G /usr/bin/otii-data/otii 72MiB |
| 0 103423 G /usr/lib/Xorg 202MiB |
| 0 103495 G /usr/bin/kwin_x11 212MiB |
| 0 103550 G /usr/bin/plasmashell 135MiB |
| 0 105109 G c:\Program Files\Tencent\WeChat\WeChat.exe 4MiB |
| 0 106072 G ...AAgAAAAAAAAACAAAAAAAAAA= --shared-files 102MiB |
| 0 106544 G ...AAgAAAAAAAAACAAAAAAAAAA= --shared-files 47MiB |
+-----------------------------------------------------------------------------+
+-----------------------------------------------------------------------------+
| Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| 0 543 G /usr/lib/Xorg 825MiB |
| 0 1289 G /usr/bin/kwin_x11 127MiB |
| 0 1333 G /usr/bin/plasmashell 118MiB |
| 0 82335 G /usr/bin/systemsettings5 127MiB |
| 0 90480 G ...AAgAAAAAAAAACAAAAAAAAAA= --shared-files 46MiB |
| 0 94865 G /usr/bin/otii-data/otii 72MiB |
| 0 103423 G /usr/lib/Xorg 202MiB |
| 0 103495 G /usr/bin/kwin_x11 212MiB |
| 0 103550 G /usr/bin/plasmashell 135MiB |
| 0 105109 G c:\Program Files\Tencent\WeChat\WeChat.exe 4MiB |
| 0 106072 G ...AAgAAAAAAAAACAAAAAAAAAA= --shared-files 102MiB |
| 0 106544 G ...AAgAAAAAAAAACAAAAAAAAAA= --shared-files 47MiB |
+-----------------------------------------------------------------------------+