Cannot download new apps; GET button spins

Here are a variety of resources helping with connectivity issues:

Restart your equipment and/or sign out and back in again, and try again. When using a computer you can also try SafeMOde —> Start up your Mac in safe mode - Apple Support

Choose your macOS version at the top.

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

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 you can't connect to Wi-Fi on your iPhone or iPad - Apple Support

Try resetting only network settings (again, be careful what you reset here!):

Reset iPhone settings to their defaults - Apple Support

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

Remove the VPN entirely, don't just turn off.

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 Support - Apple Support

This person ( https://discussions.apple.com/thread/256237834 ) found that resetting their iPhone to factory settings allowed access, but that is a pretty extreme solution.