Qt Designer has no canvas

Hello,
I create a Qt Quick Application

Build system: qmake

Minimum required Qt version: Qt 5.15

Kit: Desktop Qt 5.15.2 MinGW 64-bit

First time I couldn't use the "Design" tab on the left. I went to Help->About Plugins->I search Qt Quick and I check the box "Load"->I clicked OK button.

When I clicked "Design" tab ->pup up 3 windows with the project... weird!

I close "X" one of the windows and all of them disappear...

I tried to find my window  but no chance...

I research a bit on google and seems a error "Qt Designer has no canvas"

Thank you in advance for any suggestions to fix the issue..