How can I cancel select text operate?

when i press “shift” and click inside editor, the part between the cursor and where I clicked will be selected
like this
image
but when i click outside editor, why does the selection operation still occur? In fact, I want to cancel the selection
like this
image
how can i prevent this default operation

That appears to be native browser behavior (on Chrome, Firefox doesn’t do it). It’s not related to events that target the editor (given that the click happens outside), so I don’t think there’s much the library can do about this.

Can I modify the key that triggers this selection event, such as the cmd key instead of shift key?

I noticed that there is such a configuration as rectangularSelection in the manual
Whether this configuration item can intercept selected events

Not for the browser’s native behavior (which, again, is what you’re seeing here), no.