Hi,

There is already a function called "onSelect" in Many2XAutocomplete component so you can use that by patching it.

/** @odoo-module **/
import { Many2XAutocomplete } from "@web/views/fields/relational_utils";

import { patch } from "@web/core/utils/patch";

patch(Many2XAutocomplete.prototype, "file_path or something unique", {
    onSelect(option, params = {}){
        // your code
        this._super.apply(this, arguments);
    }
})

Regards