When you load an lwc component that is a screenAction, when you click a button to activate component or is triggered via a connectedCallback, this alway appears.
How would you hide the white background?
I know you can do an slds-hide a a specific Div, but what would this count as?
Unfortunately, you can't do this in an approved manner. It's baked in to the modal's styles. You can use loadStyle to globally override CSS (e.g. the modal's background), but this may be blocked in a future update. Ideally, you should just accept that the background is a necessary limitation of the platform. Any workaround you may do for now will not likely last for long into the future.
