Apple mobile devices back in the day never had a lot of RAM. And it never needed them, considering that the mobile OS are so optimised. But as newer devices come with more, a strange limitation of iOS and iPadOS have since surfaced. The restriction here is that apps could never make use of more than 5GB of RAM. And Apple is working on removing this limitation.
In the second version of the iOS and iPadOS 15 beta versions, developers were allowed access to the extra RAM via an entitlement code. This will allow the app to tell the operating system that it can work better with the extra resource.