Apple is focused on privacy for kids and authentication methods acceptable for apps listed in the App Store. The default position for apps in the App Store is that they must use the Sign in with Apple authentication method. Exceptions to this rule exist. Apple has added a host of kids' protections.
After a year plus deprecation period and one extension to the official cutoff date, Dropbox has officially retired the Dropbox API v1. v2 has been live for quite some time and Dropbox has been promoting its consistency, simplicity, and scalability to entice developers to move to the new platform.