I am assuming you have a NOW branded box ?
The original NOW black box and NOW 4K Smart box should still support the Disney Plus App, together with the NOW Stick.
Should you be unfortunate to own a NOW Freeview Smart box with the blue NOW TV name on the top casing, then this box lost support for the Disney Plus App back in May 2023 and you will have to look at other playback devices to watch Disney Plus.
Here's the supported devices taken from the Disney + website.
Should you click on the NOW devices link, ignore the NOW Freeview Smart box which isn't supported anymore, where Disney + haven't yet removed it from their list.
Where I tend to use my Roku Stick Plus, Amazon 4K Fire Stick and Chromecast Google 4K TV when watching Disney on the Disney + App.