Hello
Thank you for posting in Microsoft Community forum.
Here's how you can disable the "square line" effect when moving tabs:
1.Open System Properties:
Press Win + R to open the Run dialog box.
Type sysdm.cpl and press Enter.
2.Adjust Performance Settings:
In the System Properties window, go to the Advanced tab.
Under Performance, click on Settings.
3.Visual Effects:
In the Performance Options window, select the Visual Effects tab.
Choose Adjust for best performance to disable all visual effects, or you can manually uncheck specific options like "Show window contents while dragging".
4.Apply Changes:
Click Apply and then OK to save your changes.
This should help make moving tabs smoother and remove the annoying square line effect.
Best Regards,
Wesley Li