If you mean the home screen, it’s a feature enabled by the server. On Windows there’s a “hack” to revert to the classic one, open ZwiftApp.exe with an hex editor (like HxD), search for the feature name (game_1_20_home_screen) and change any character.
What are you running Zwift on? The new home screen was rolled out and then rolled back on some platforms (eg, Android 13). Long term you will not be able to keep the old home screen.
No, i had exactly the same thing on Wednesday at about 1300GMT (running W10); though I closed and reopened Zwift almost immediately and had the new homescreen return.