MacRumors published a story that Apple has released the second release candidate of iPadOS 15.1 for the iPad Mini 6 to registered developers.

Apple Seeds Second iPadOS 15.1 Release Candidate for iPad Mini 6

Apple today seeded a second release candidate version of iPadOS 15.1 to developers for testing purposes, with the update coming just a few days released the first RC. This RC is only available to those who have an iPad mini 6, and there is no accompanying iOS 15.1 RC 2. Registered developers can download the iPadOS 15 RC from the Apple Developer Center, and once the profile is installed, beta updates will be available over the air. 

Apple Seeds Second iPadOS 15.1 Release Candidate for iPad Mini 6