Hello,
require([
'jquery',
'Magento_Customer/js/model/authentication-popup'
], function ($,auth) {
auth.showModal();
// if you want to check customer is not login then open
// if(auth.isActive())
//{
// auth.showModal();
// }
});
if works then mark as solution.
Problem solved? Click Kudos & Accept as Solution!
Sunil Patel
Magento 2 Certified Professional Developer & Frontend Developer