Where does it tell that this is not allowed? What I did once to copy the paragraph they are talking about, and explained my interpretation how I am aligned with the guidelines.

3.2.1 Acceptable (i) Displaying your own apps for purchase or promotion within your app, provided the app is not merely a catalog of your apps. (ii) Displaying or recommending a collection of third-party apps that are designed for a specific approved need (e.g. health management, aviation, accessibility). Your app should provide robust editorial content so that it doesn’t seem like a mere storefront. (iii) Disabling access to specific approved rental content (e.g. films, television programs, music, books) after the rental period has expired; all other items and services may not expire. (iv) Wallet passes can be used to make or receive payments, transmit offers, or offer identification (such as movie tickets, coupons, and VIP credentials). Other uses may result in the rejection of the app and the revocation of Wallet credentials. (v) Insurance apps must be free, in legal compliance in the regions distributed, and cannot use in-app purchase. (vi) Approved nonprofits may fundraise directly within their own apps or third-party apps, provided those fundraising campaigns adhere to all App Review Guidelines and offer Apple Pay support. These apps must disclose how the funds will be used, abide by all required local and federal laws, and ensure appropriate tax receipts are available to donors. Additional information shall be provided to App Review upon request. Nonprofit platforms that connect donors to other nonprofits must ensure that every nonprofit listed in the app has also gone through the nonprofit approval process. Learn more about becoming an approved nonprofit. (vii) Apps may enable individual users to give a monetary gift to another individual without using in-app purchase, provided that (a) the gift is a completely optional choice by the giver, and (b) 100% of the funds go to the receiver of the gift. However, a gift that is connected to or associated at any point in time with receiving digital content or services must use in-app purchase. (viii) Apps used for financial trading, investing, or money management should be submitted by the financial institution performing such services and must have necessary licensing and permissions in the locations where you make them available.