Apple ID not yet been used in the iTunes Store
I'm unable to download any apps due to the Apple ID not yet been used in the iTunes Store.
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The resolution to this issue is often making sure you have entered a credit card or other valid method of payment even if you don't plan on needing to use it. The document 'If you can't remove your last payment method or use no payment method with your Apple ID' mentions "if you're using an existing Apple ID with the App Store for the first time, you must provide payment information," in this link: https://support.apple.com/HT203905
If there is an option to select "Review" or "Continue", select that and enter valid payment information if required. If there's problems doing this:
Tap: Settings > [your name at the top] > Media & Purchases > View Account > Review Apple ID.
More things to try in this 2018 post by Urquhart1244 marked Apple Recommended:
https://discussions.apple.com/thread/8434425?answerId=33542414022#33542414022
Payment methods that you can use with your Apple ID - https://support.apple.com/HT202631