Create Apple ID without payment method
How to download apps without payment method
iPhone 7, iOS 15
"To make purchases from the App Store and use subscriptions like iCloud+
and Apple Music, you need at least one payment method on file."
Add a payment method to your Apple ID - Apple Support
//support.apple.com/en-us/HT201266
Needs one added, even if you aren't going to purchase anything.
Also some apps 'offer extras', & those require payment scheme.
Other details apply when you choose to change payment method.
If you need to change or update your Apple ID payment method - Apple Support
//support.apple.com/en-us/HT213276