-1👍
Yes, you can set the group-expand prop to "true" to make the groups expanded by default. You can add this prop to your v-data-table component.
<v-data-table
:group-by="groupBy"
:headers="headers"
:items="desserts"
:sort-by="sortBy"
class="elevation-1"
item-value="name"
group-expand
></v-data-table>
Source:stackexchange.com