You can just push multiple files in an array.
<template>
<form @submit.prevent="submit">
<input type="file" @input="form.files = $event.target.files" multiple/>
<button>Submit</button>
</form>
</template>
<script setup>
import { useForm } from '@inertiajs/inertia-vue3';
const form = useForm({
files: [], // <-- array
});
function submit() {
form.post('/upload')
}
</script>
Then in Laravel access normally by:
$request->file('files'); // <-- array