There are several key concepts that require clarification in this discussion.
“Scoped slots” (or simply “slots” in the context of Vue 3) have the ability to transmit data to the parent component. Imagine the slot as a sort of function with parameters. Here, the activator slot within the <v-dialog> is sending an object with properties like on and attrs for use within the slot content template. It's important to consult the documentation for <v-dialog> to understand how this data should be utilized; in this instance, <v-dialog> needs to detect when the activator is clicked to display the dialog, hence why it provides access to on and attrs which must be linked to the custom button designated as the dialog activator.
In many component libraries, it is common for slots to provide access to on (event listeners) and attrs (attributes/props) required by the component to be set on another component in the template; this can be achieved using v-on and v-bind respectively. Review the documentation to see how these directives can be used to bind multiple attributes simultaneously, for example:
<!-- binding an object of attributes -->
<div v-bind="{ id: someProp, 'other-attr': otherProp }"></div>
The specific syntax utilizing object destructing:
<template v-slot:activator="{ on, attrs }">
<v-btn v-bind="attrs" v-on="on">
is equivalent to:
<template v-slot:activator="scope">
<v-btn v-bind="scope.attrs" v-on="scope.on">
The properties on and attrs are simply being separated into distinct variables for easier access.