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I think you do wrong over here : you need to write /view/frontend/web/template/checkout/check-login-view.html instead of /view/frontend/web/template/checkout/check-login-view.js

also chagne over here.

          stepNavigator.registerStep(
          
            'check_login',
            //step alias
            **'check_login'**,//you forgto to add ''(single quote)
            //step title value
            'Login / Registrati',
            //observable property with logic when display step or hide step
            this.isVisible,

            _.bind(this.navigate, this),

            
        );