What user info does Apple disclose to third party app developers, once a user purchases an app?

what kind of privacy related info is exposed to third party app developers, if I downloaded and purchase their app?

For example:

• Physical SIM card info (e.g, Phone number)

• iPhone board info (e.g, IMEI number)

• My Apple ID

• My name and address that I provided Apple as part of the required additional payment information (Like shipping address, even though the apps are not getting "shipped" to me, or my PayPal email address)

• My MAC address (can it be blocked on iOS 14?)

• Info related to the Wifi router I often connect to at my home

• Cookies and cache - How may I track and delete them? for example, I deleted an app that had permission to use my location, but when I re-downloaded it, I didn't have to give it permission again, which means there is some kind of cache somewhere.

I want to get a very clear picture of what kind of info those apps can collect and store about me to identify me in future time.

This is also relevant in case someone buys a used phone, what steps are required to start a "fresh" page when it comes to any of such apps, so the user does not get confused with the previous owner?

What user info does Apple disclose to third party app developers, once a user purchases an app?

The short answer is it depends.

It depends on what the App developer claims it needs to collect. Apple doesn't sell your data nor will it give out data "willy nilly." But if a product/service that you want requires the sharing of data, Apple will share it.

From Apple's Legal page concerning Privacy:

Disclosure to Third Parties

At times Apple may provide third parties with certain personal information to provide or improve our products and services, including to deliver products at your request, or to help Apple market to consumers. When we do, we require those third parties to handle it in accordance with relevant laws. Apple does not sell personal information, and personal information will never be shared with third parties for their marketing purposes. For example, when you purchase and activate your iPhone, you authorize Apple and your carrier to exchange the information you provide during the activation process to carry out service, including information about your device. If you are approved for service, your account will be governed by Apple and your carrier’s respective privacy policies.

To put this another way - Apple will share what is necessary to provide you with the product/service you're requesting. If there is a 3rd party, your private info they have will be governed by their privacy policy.

As for your data with respect to individual apps, what gets shared depends on what the App itself is requesting. However, it's Apple's policy that you be made aware of what personal info the app requires

App guidelines

On the App Store, Apple requires app developers to adhere by specific guidelines designed to protect user privacy and security. Apple also requires them to provide a privacy policy that you can review. When Apple becomes aware of an app that violates our guidelines, the developer must address the issue or the app will be removed from the App Store. Apps go through a review process before becoming available on the App Store.

^{(Emphasis mine)}

In short, the App you purchase can obtain/use any/all the information you described in your question. However, they must make you aware of it. They may not need nor do you want an App to have have access to PayPal addresses, however, if the App says they collect it, they can. If they do collect it and don't tell you that would be a violation of Apple's Privacy Policy.

On the other side of that coin, your data that they collected (in accordance with Apple's policies) are now governed by their privacy policy. So, if on the App store, they say that they collect your personal information like a Social Security number, and then turn around and sell it, they may be well within their rights to do so if that's what it says in their policy.

Bottom Line

Before purchasing/installing an app, check to see what info the app collects. Many people marvel at how many free apps there are on the App store not realizing the hidden cost - their privacy. App developers want to get paid for their work and if they're not charging you anything up front or have in-app purchases, the app isn't the product they're selling - you are.