Can’t open apps on iphone

It may be your app is offloaded to save space. How to check the storage on your iPhone and iPad - Apple Support

You need to download it. With the problem you describe it sounds like a connectivity issue. Here are a variety of resources helping with connectivity issues:

If you can't connect to the App Store, iTunes Store, or other Apple services, read this support article --> If you can't connect to the App Store, iTunes Store, or other Apple services - Apple Support

- If none of the suggestions work, try the last one: "If you’ve tried all of the above steps and you still can’t connect, contact Apple Support."

Here's a related article about what to do if you can't connect or sign in to iCloud --> If you can't connect or sign in to iCloud - Apple Support

If your iPhone or iPad won’t connect to a Wi-Fi network, or if you have related connectivity issues, read this support article --> If your iPhone or iPad won't connect to a Wi-Fi network - Apple Support

Here's a case where using a VPN prevented sign-in --> AppStore - Apple Community

If none of the resources provide a solution, contact Apple for assistance:

For support, click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world."

Click here --> Contact Apple for support and service - Apple Support