you can take the following course, which contains creating a custom login page: https://gettingstarted.mendixcloud.com/link/path/56/Create-an-App-with-Advanced-Page-Building
You can customize this as you like. You will see the left background image has class ‘loginpage-image’ and the loginpage’s logo has class ‘loginpage-logo’.
Heyy, I see that this topic is already a little old but my problem is the same. Did you solve it?