If Salesforce removed in summer 20 version.. Any alternate way for "Mobile user" checkbox feature that exactly provided. i.e (mobile experience to the user)
As per https://help.salesforce.com/articleView?language=en_US&type=1&mode=1&id=000349471 , starting Summer'20 Mobile Web Experience would be retired. The alternative that salesforce suggests is to use Salesforce Mobile App.
Starting in June, 2020, you need to have the Salesforce mobile app installed on your device or use Lightning Experience on iPad Browsers.