CRTL-B hangs my system

I tried the Crtl+B on two selected objects to open the Boolean Assistant, which it did.
However, I couldn’t get it to move “behind” anything on a single monitor.
For me, that dialog box forces itself “on top” until closed.
And just like the OP, I get the warning bell if I select anywhere other than one of its options and Okay or Cancel.

Do this, hold down the Alt key and Press the Tab key. You should see the open applicatons cycle with ever single pressing of the Tab key. All of the open apps should be visible, so you can just keep pressing the Tab key repeatedly to go to the next app.
Look for the Boolean Assistant dialog as if it were its own application.

Again, for me, it was only visible when I had LightBurn as the currently selected app AND it was always on top or alongside of LightBurn if I had LightBurn half sized on the monitor.