Nearly every other UI framework has established disabling scroll of the page as the user's focus is the current dialog or window that is opened.

You can see this in various examples listed below:

• https://getbootstrap.com/docs/5.3/components/modal/
• https://www.matblazor.com/Dialog 
• https://mudblazor.com/components/dialog
• https://chakra-ui.com/docs/components/modal
• https://material.angular.io/components/dialog/overview

As such I would expect the same behavior as this in my experience is the industry norm.

-----ADMIN EDIT-----

As a possible alternative, to disable the modal window background scroll, you can use the following conditional CSS:

@if(IsModalVisible)
{
    <style>
        body {
            overflow: hidden;
        }
    </style>
}