my_item.vue

<template>
    <a-col v-bind="attr">
        <a-form-model-item v-bind="layout">
            <slot />
        </a-form-model-item>
    </a-col>
</template>

<script>
export default {
    props: {
        colAttr: {
            type: Object,
            default: undefined,
        },
    },
    data() {
        return {
            attr: this.colAttr ? this.colAttr : { xs: 24, sm: 24, lg: 12, xl: 6 },
            layout: { labelCol: { span: 6 }, wrapperCol: { span: 18 }, ...this.$attrs },
        };
    },
};
</script>