Sure, 4K exists. But for a film made in 2001 (pre-digital domination), 720p offers a perfect balance:
You can watch the official English-dubbed version at 720p or 1080p resolution on these platforms: spirited away english dub 720p movies hot
To get the best quality (720p and above) and support the creators, you can find the English dub on several official platforms: Sure, 4K exists